>>13167430>>13167434>>13167438The Slavs spread very far. They even captured enough territories from the Byzantines in Greece that they had to assimilate the Slavs into Greek culture when they reconquered it, they even sent some Slavs to Asia Minor. That's where the theory of them bein Slavic comes from.
From genetic research Hungarians, Romanians, and Bulgarians share a significant relation to Slavs. Greeks share a much smaller admixture.
https://en.wikipedia.org/wiki/Slavic_migrations_to_the_Balkanshttps://en.wikipedia.org/wiki/Asia_Minor_Slavs 