In Slavic languages surnames coming from adjectives are quite common. My knowledge of Russian is not big enough to explain it on that but in Czech for instance there are surnames based on location, by the city or so, so when there is for instance city of Hradec, you can find a surname "Hradecký" (belonging to/coming from Hradec). It doesn't has to be a municipality but also some area, let's say "Black Mountain", Černá hora, so someone from there has surname "Černohorský".
Or it can be an allusion to some feature of parents, here we have example in Maiia Khromykh. Khromyi is lame in Russian, but it's not like the bearer of that name is lame himself, but you can think that it is a person whose parents were "lame", so Khromykh is like "belonging to lame" (like those lame who live there over the river, I presume the genesis of that surname was something like that".
Bregei I suspect it could come let!s say from "bereg", bank, so someone who lives near a bank of a river, lake or so.