It seems that things are complicated by the fact that initially Stalin did pressure Mao against resuming the Civil War and refrained from aiding him up until Chinese Communist victory become obvious from the victories in 1948. He is quite on the record of admitting in early-1949 to a visiting Chinese envoy that he had underestimated the Chinese communists strength and apologized for the lack of aid.
It is true that in 1945 Stalin cautioned Mao against starting a civil war prematurely (Mao had wanted to seize major cities after the Japanese surrender before Chiang's forces could get to them) but it is not true that Stalin did not aid the CCP until 1948:
"In Manchuria, the CCP immediately began the process of incorporating 75,000 former Manchukuo puppet troops into its forces as well as thousands of other fresh recruits from the mass of unemployed Manchurian youth and the 80,000 or so bandits roaming the mountains. Meanwhile, the Soviets were quickly turning over to the Chinese Communists a huge collection of liberated Japanese weapons and military supplies. The Red Army sent the more advanced weapons and machinery back to the USSR and kept older Japanese tanks and artillery in an arsenal on the Sino-Mongolian border at Manzhouli to be turned over later. They also gave the Chinese Communists a number of captured Japanese armament factories, and the CCP itself found several underground arsenal that the Soviets had missed.
"With reports probably provided by Okamura, Chiang knew how many Japanese weapons and other items the Soviets had captured. In addition to huge numbers of rifles, ammunition, grenades, and small mortars, the take included 925 fighter planes, 360 tanks, 2,600 cannon, 8,900 machine guns, 100,000 horses, and 21,000 'logistical vehicles.' Chiang of course inherited probably even larger arsenals from those Japanese south of the Great Wall. Contrary to Mao's later insistence that after V-J Day Stalin abandoned the CCP until the fall of 1947, books from the Publishing House of CCP Historical Materials, articles in official Chinese Communist journals, as well as Soviet archival material recount at length the extensive and deep Soviet-CCP cooperation that began with the Soviet Red Army invasion of Manchuria. In late August, however, Stalin kept up the charade, telling Harriman that the Red Army in its sweep through Manchuria had not encountered any Chinese Communist forces. Stalin said he expected the Chinese government would soon send troops to take over the Manchurian cities..."
https://books.google.com/books?id=DUg2KGMQWHQC&pg=PA317 https://books.google.com/books?id=DUg2KGMQWHQC&pg=PA318
Stalin's goal in 1945 was to get US troops out of China as soon as possible, and for that reason he had to project the image of supporting a united China under Chiang Kai-shek's leadership. But at the same time he was giving substantial if discreet aid to the CCP. This aid continued in 1946-47. As summarized by Michael M. Sheng,
Battling Western Imperialism: Mao, Stalin, and the United States, pp. 155-6:
"The other side of the coin of CCP hostility toward the United States was the intimate relationship between the CCP and Moscow, which both sides involved tried to conceal as much as possible. In the face of the GMD-CCP civil war raging throughout the nation, the United States continued to assist the GMD overtly, while the Soviet Union was covertly backing the CCP with military supplies and diplomatic coordination. This CCP-Moscow vs. GMD-Washington conflict continued throughout 1946-47, which was an important part of the hidden history of the cold war in Asia.
"According to recent CCP sources of information, Soviet material support to the CCP after the withdrawal of the Red Army was essentially delivered from the city of Dalian and North Korea, both of which were under Soviet direct control. For instance, Xiao Jingguang, the deputy commander of CCP forces in Manchuria, went to Dalian in July 1946 to arrange the Party's military production in the city. At the time, the GMD had occupied the south of the Songhua (Sungari) River, which made it impossible to keep the CCP troops in southern Manchuria supplied from the northern base. The only point in southern Manchuria which could keep producing military supplies for the CCP forces was Dalian, because it was occupied by the Soviets. Xiao went there, and was pleased to find that, from the head of the police force to the head of the financial department, all administrative posts of the municipal government were in the hands of Communist cadres. Relying upon the. cadres, CCP military production in that city was well maintained throughout the period of the civil war. There are no available statistics on the volume of Dalian's military production for the CCP's war effort during these years. According to Xiao, however, it made a great contribution to the victory in the Liberation War'.
"The other place which served as the source of the CCP's military supplies was North Korea. After his trip to Dalian, Xiao spent two months in North Korea to establish the 'Delegation of the Northeast Bureau to Korea' (
Dong-beiju zhu chaoxian banshichu), known publicly as the Pyongyang Limin Company. It had four branches in Korea, whose main task was to organize the supply, storage, and transportation of military materials for the CCP forces. Zhu Lizhi, later the deputy of the Logistics Department of the CCP forces in Manchuria, was in charge of this 'Limin Company.' The number of people working in one of the branches exceeded five hundred at one time. According to incomplete statistics, in the first seven months of 1947, there were 210,000 tons of war materials transferred to the CCP through North Korea. The figure in 1948 increased to 300,900 tons. Before the 'Company' was closed in February 1949, it obtained enough military cargo from the Soviet—North Korea source to fill more than 2,000 rail cars to ship to Manchuria. It also helped the CCP Shandong logistics department to buy and ship military supplies from North Korea...."
As Sheng notes (p. 15) "In numerous occasions after Stalin's death Mao purposely discredited Stalin's contribution to the CCP cause, thereby creating a myth that Stalin was always wrong in his China policy, and Mao was always correct and he resisted Stalin and saved the CCP revolution single-handedly. The myth of Mao's own making has been influential in the western scholarship in the field..."
https://books.google.com/books?id=HZJcxq1DIOYC&pg=PA15