I wouldn’t recommend using Bozho as a source – if he was ever a serious scholar, he has long ago put that behind him and is now riding the wave of the pseudo-patriotism (and, potentially, commercialism, especially in regards to his hometown of Sozopol). Especially in regards to the truly messy subject of the origins of the Bulgars, which is a matter too uncertain even for the best of the best among the serious historians. And there’s quite a number of expectable factors for this, of course – starting from simple propaganda (history is a favourite tool in the hands of politics, especially in this region of ours, and flows in several directions even today), going through the complexity of the matter (what defines our identity – is it our language, our name, our genes, our culture, our religion, our political allegiance? That’s complicated enough even if it’s only about the modern Bulgarians, now think about how even more complicated it is in the medieval reality) and finishing, among others, at the unfortunate scarcity of the potential sources.