A very similar thing happened to me a few months ago. A couple of years ago I had written a certain small piece of web software (about 1.2k lines long) and put

A very similar thing happened to me a few months ago. A couple of years ago I had written a certain small piece of web software (about 1.2k lines long) and put it on GitHub. On Wikipedia, I saw that there was some software which did the same thing, which I'd never heard of before. Interested to see how it was implemented, I browsed the files in their GitHub repo and saw my exact code in there, with a few tweaks and improvements made by someone else. I didn't appear to be credited. This was all complicated by the fact I released the code initially under a public domain license. However, I forgot that I used a small snippet of some GPL code, and re-licensed to GPL a few days later. Unfortunately, I hadn't made any concrete change to the code after relicensing, so I couldn't tell if the public domain version or the GPL version of my code was 'stolen' (for lack of a better word). When I alerted the project owner about this matter on their Discord server, with all the good will I could manage (the only way I could find to contact them), a sizable project of ~20 people, my message was deleted and I was banned. In the end, they added credit to me for the code (and my code was their entire project, plus some bugfixes), but I don't think they relicensed to GPLv3. I doubt the author of the GPL'd snippet would bother to pursue it.