No? Serbia had originally asked Bulgaria to commit more troops to the Macedonian theater - and Bulgaria refused. Later, the Bulgarian military leadership's view (focusing on Thrace) was accepted by both countries, and adopted into the joint war plan.
(And this was a more or less reasonable view. I mean, what happens if they do neglect Thrace in favor of Macedonia? The Ottomans could bring in reinforcements from Asia into Thrace, throw the Bulgarians back by sheer weight of numbers, and attack Bulgaria itself. Quickly and decisively crushing the Ottoman forces in Thrace was pretty important for Bulgaria.)