My grandmother calls herself a Yugoslav too, I've never had a problem with the word and she's no Commie (although my aunt is -or was)
It may be that even though her family comes from a Serbian ethnic background they were converted (rather nominally) at some point but then it doesn't make them Bosniak either. Ah, the Balkans.
Anyway, the thing is, the Yugoslav ethnicity being almost limited to a specific area is rather strange, at least to me.