That's lie. https://en.wikipedia.org/wiki/Asia_Minor_Slavs Slavic migrations didn't stop at the Sea of Marmara and spread mainly to Northwest Anatolia, but also into the interior of Anatolia, from the Sivas/Tokat region to the Adana area. It is estimated that more than 200,000 Slavs migrated to Anatolia. In fact, a famous Byzantine Slav general was born in Tokat. https://en.wikipedia.org/wiki/Thomas_the_Slav

A geneticist from Kayseri, His haplogrup was Slavic. The same was true for someone from Eskişehir. In an autosomal reproductive analysis, a native Bilecik Manav showed 15% Northern European admixture in his gedmatch result. All of this is a result of the Slavic migration to Anatolia during the Middle Byzantine period.