You remember cossacks, last seen talked about as a deliberate symbol here http://secondcrimeanwar.thecomicseries.com/comics/205/ and how Bohdan took his name from a cossack rebel against the rich landowners of the Polish-Lithuanian Commonwealth? Yeah, so you had the 'free cossacks' who ran off to the Wild Field. And on the flip side, you had 'registered cossacks' who were in the pay of the settled ruling classes. Yana is saying from Bohdan's men's perspective, she's a modern counterpart since she works, however distantly, for the official regime.
And before I get hate mail*, I know "Slav" isn't derived from "slave". (It's the other way around, as it happens.)
*I kid, you guys are awesomely civil while correcting me as needed.