Chances are someone you link to (either following their channel or through some other metric) has engaged with that content, and so Youtube believes that you're more likely to engage with it as well, if you have overlapping interests. It may be a relationship several orders removed from you - but Youtube still counts it.

> If anything, because I was so puzzled by what was happening that I looked at who this Leather fellow was, Youtube’s trillion dollar “AI” tech stack will probably serve more and more of this stuff.

So... it worked. You seem to be confused about the goals of Youtube's algorithm - it isn't to show you the content you're most interested in, per se, it's to show you the content you're more likely to add value to by engagement. That can and often does correlate to your interests, but controversy works just as well, which is why these platforms often incentivize controversy over quality. Sometimes they'll throw random stuff into your feed just so see if you'll bite.

Consider deleting your view history if you haven't already. Go through your subscriptions and see who they're following. Absolutely do not click on more than one of someone's video if you don't want to get flooded with their content.