You see this with Amazon and eBay too - if you search Google for something weird which no one has bid on, you'll often see "Find [bananaphone] on eBay/Amazon". These "people search" results are similar: extremely long-tail, very generic ad.
So, I think its probably algorithmic vs intentional. Could be ML that's learned racism from the internet itself.
Who knows though! Your explanation would certainly make sense. Its a fascinating problem.
This was my first thought.
Google is involved to the extent that they serve ads in response to specific keywords. Instant Checkmate is involved only to the extent that they ignore the source of their referrals. Someone with a little more free time could probably trace HTTP traffic to find the specific affiliate responsible.