I have to admit that I chuckled when I saw your thread since the Socialist Federal Republic of Yugoslavia tends to be a heated topic for socialists, but to answer your question: it depends on your criteria. If you define communism as a classless, stateless, moneyless existence distinct from socialism, then the SFRY wasn’t communist, but you could say that about any other people’s republic, and I think that that’s a moot, uninteresting point to make anyway.
If you define socialism as the negation of capitalism — that is to say, the negation of capital, the law of value, and generalised commodity production — then I’d categorize the SFRY as merely presocialist (as silly as it may sound to call a self‐described Socialist Republic ‘presocialist’).
After the Soviet stance on the Greek civil war alienated the Yugoslavs, the SFRY adopted a sort of semiplanned economy where market mechanisms continued to exist (hence why some pro‐Soviet communists consider the SFRY capitalist). This was not so much because Yugoslav politicians now rejected scientific socialism, but because the SFRY’s isolation from the rest of the Eastern Bloc made it an inevitability. There is a great book titled Class Struggle in Socialist Poland that delves into the subject of the SFRY’s market mechanisms, but I can’t give you a link yet since Archive.org is partially down.
The lower classes won some very important gains because of the SFRY (as they did in the other people’s republics), so as much as I can sympathize with the left communist tendency to categorise these republics as ‘capitalist’, I can’t heap scorn on them either. That would be like rolling my eyes at strikers for winning concessions when they ‘really’ should be abolishing capitalism, but now I’m just rambling.