Pre-1990, Bosnia was not majority-muslim either. It never was. And before the islamist and ustashi genocide of the Serbian people during WWII, Bosnia (then merely a region of Yugoslavia, as it rightly should be) was majority Orthodox Serb.
And prior to and during WWI, some Bosnian muslims were participants in Serb nationalist organizations that called for the liberation of Bosnia from Austria-Hungary, and its integration with Serbia.
Never said it was a majority, just not another unique ethnic group as Tito tried to sell it.