Do you just suck it up and try to feel flattered?

Basically my little brother organised some bizarre 8 bit compilation last year which he released for free online, then he found out today that someone has mysteriously pressed it to vinyl and it's being sold in record shops across the UK, US and Japan.

Found out who the distributor is and sent him in email in order to find out who's responsible for the pressing, but then what? Is it worth even asking this guy to stop selling it when he's most likely making no money off it himself? But then on the other hand it's kind of annoying that none of the artists were asked about this, cause they obviously would all have said yes.

What's the "I've been bootlegged" etiquette?