Bylazora is only one of the many toponyms in the Balkans than sound way to Slavic but predate anything that might connect them with the Slavs.

Note the ancient name of Skopje – Scupi. Sounds similar to skupa, skup, kup etc. Or the capital of the roman province of Macedonia – Stobi. Stolb, stob, stub is a common name for a pillar among Slavs. Pella, the capital of the ancient Macedonian kingdom might have been derived from spela / spila , a big rock, and this is a toponym found on several places on the Balkans.

Also, one must have in mind that we only know these place name as taken from Greek or Roman sources. Their original names were probably changed a bit in order to fit the Greek or Roman pronouncing system.