Earlier quoted context omitted.
To be frank, I don't think you've actually conducted an empirical comparison of "black male + white female couplings IRL and in the media", nor do I think such a discrepancy would be worthy of comment even if it exists, and perhaps most importantly, I do not believe in the innocent motives of anyone who brings up the subject and then acts like they are only attempting to make an innocuous anthropological observation.…
In defense of the guy that brought it up: race-mixing is a huge scissor statement. It's already working here - you're getting your socks in a tizzy over a mention of it and can't get past the object-level. The meta-level is it doesn't matter what concept they use - race, gender, sex, identity - posters can and will use it to make you fight people you would otherwise get along with.
As for the scissor statements, here's another good one: 'Women have smaller brains than men'. It is true (on average) but it will draw out mouth-frothing SJWs without fail.