"Open source" as a term has evolved due to its success. It wasn't some malicious attempt at redefining things from the technical elite. It was a natural shifting of language, as happens with all words, as it entered more common usage.

It's entirely reasonable that this colloquial understanding would be applied to new categories such as AI models. I'm sure it'll be applied to many other things that don't fit the OSD either. That's just language for you.