no they are not, there is huge overlap between serbs and rum/bulgarians, while only few stretch to the edge of bosniaks, probably bosnan serbs who today live in serbia, because there is lots of migration of bosnian serbs to serbia
Besides their native base was the same, tracians, during age of byzantium, serbs were belived to be tribali by greek historians, a tracian tribe, also first Serbian state Rascia is teritorialy the same Tracian tribali teritory
That's not what the actual study says. Look better at the ADMIXTURE analysis.