It's not clear what tort would be committed under US law by someone who sold injection-molded parts using the Gridfinity STLs. Patent infringement? No patent has issued. Copyright infringement? Copyright generally only covers expressive elements of works such as the sculpture in question, not functional elements like the "Sega" string that was at issue in Sega vs. Accolade. Trademark? Also doesn't protect functional elements.

Basically, it seems like the inventor purports to be licensing the kinds of exclusive rights to their invention that a patent would grant them, but without actually meeting the legal requirements for receiving a patent.

(I don't know of any other jurisdiction that would give them a cause of action either, but law is diverse enough, and many governments are corrupt enough, that I'm sure there's somewhere in the world they could win a lawsuit.)

Maybe some actual lawyers could chime in on this.