This is hilarious, but I think the most mature thing to do would have been to detect if the site is inside an iframe and if so add a polite link saying "click here to go to sqword.com and play this game ad free".
I get the sense that that isn't really his goal. He makes clear it's just a fun passion project, and this sounds like an equally fun (to him) way of retaliating against those taking advantage of it.
He mentioned that he found the imposters when a coworker happened across them on a search result page. Does Google apply penalties to the imposter sites’ search rankings when they serve shock content rather than what was being searched for?
It seems like that might reduce real users’ confusion as they try to find the real “sqword” puzzle.
In a roundabout way, it likely would halt users unable to find the real domain from accessing the thieves' websites again. That narrows down the search for the real domain by one!
On the other hand, they probably will get an influx of HN users now. If they had used a tamer approach, I doubt this post would have the amount of points it has now.