Welcome to the group.
To expand on the concept of "butterflies": It is related to the claim that the way a butterfly flaps its wings in South Amarica can result in a storm forming (or not) in Asia.
Or, applied to alternate history: It is common practice to identify one single "point of divergence" (POD, an abbreviation you'll see a lot). The one change to the course of history you want to explore. Having multiple unrelated PODs in a timeline (TL, also a very common abbreviation) , along with ; and ATL = "alternate timeline") is generally frowned on.
Regarding the treatment of butterfly changes: Some people are hardcore adherents of the idea that everything that can change after the POD might or will change. That does not mean that with the survival of Julius Caesar in 44 BCE the Chinese will spontaneously start speaking Nahuatl by 100 CE.
But it means that Caesar, simply by living longer, leading legions somewhere they did not go OTL (OTL = "original time line" or "our time line" meaning "real history") and perhaps having some would-be assassins killed before they died OTL, will mix up the love life of many people. Different sperms meet different eggs, children will be born or not be born, will have a different gender or a different character.
As you can imagine, like a avalanche, this multiplies over time. In 1 CE, many people will be the same, as they were born before the POD. In 100 CE no individual should exist identical to OTL.
(Some writers assume a slow ripple outward from the place the POD occured: While Rome is affected immediately, events in China, Australia or Mexico develop mostly as in OTL.)
So, assume that as a PoD, around 370 CE something stops the Huns from turning against the Ostrogoths. An epidemic plague would probably spread to the Goths as well, and that does not fit. But maybe for some reason they start at the Lower Volga and do not turn to the West, but to the South east of the Caspian Sea and try to plunder Persia. Old Iran is well known as target for nomadic people from Central Asia.
So the Goths stay where they are and do not seek refuge in the Roman Empire. But if Persia seems weakened, a later emperor might try to conquer parts of the Persian domains, thereby overstretching.
But it is certain that these events in the 4th century will have conseqences that build up to big changes by 570, so it is very unlikely the Muhammad wil ever be born. Nor will be Theoderic, or Justinian, or Clovis, or Charlemagne.
On the other hand, nations and ethnic groups will not stop to exist. The peoples of Arabia obviously had a great potential for expansionism, and it is not likely that the non-birth of Muhammad will remove that completely. So maybe they follow a radical, anti-orthodox branch of Christianity, or some type of Manichaeism. Perhaps their leader is influenced by the Jewish faith and sees himself as the Messias, or he follows the urban deities of Old Mecca. Or he is just very charismatic and a strategic genius and not religious at all.
In such a case, if people want a shorthand for "the driving force behind ahypothetical Arab expansion in this TL", they might write alt-Islam, without spelling out its theological background.