I don't know that it tells us anything about the sub's politics. Based on where it tells us users live and spend their time, I'd go so far as to say most are white, but it doesn't say anything about that definitively.

I think what that map does tell us is that users overwhelmingly live and spend their time in the affluent neighborhoods in green on the Niche map. More importantly, though, consider all of the discussion in r/baltimore on the problems facing communities in the east and west of the city. I think that that map is evidence that users overwhelmingly don't visit those parts of town, most of them ever, which calls into question how useful their perspectives are.

Like, people in this thread are calling this a redlining map, and that could be very true, but have you tried mapping out where you spend your time and money? Evidently, it might look just like this.