It's likely some coincidence of my previous viewing history, though how woodworking, small engine repair and distributed systems pointed to grossout videos I have no idea. I've heard of at least a dozen other people that this happens to so far across a wide range of viewing habits.
Funny, when I run that search in mobile Safari, disable my ad blocker, and then request desktop site to see if I can repro, I'm immediately redirected to one of the advertised sites (a scam/fraudulent site, naturally). Another oddity to toss on the pyre.
My front-page recommendations in incognito is a completely different set of videos from my front-page recommendations in my logged-in main account, except for one (a Veritasium video with 14 million views).
So if YouTube is tracking me across incognito mode, then they aren't doing a very good job there.
Like literally, my screen only had pictures of multimeters.
For good measure I repeated the search in my main Youtube account. Same thing.