Correct. (and I know you already know this but just for the record: (Nearly?) Everybody abuses the term "open source" when it comes to models. OSI have a post about it: https://opensource.org/ai/open-weights

Although it is not OSI approved, the license theoretically didn't add any more restrictions beyond attribution, which stays in line with The Open Source Definition.

That's debateable. How about, e.g, "10. No provision of the license may be predicated on any [...] style of interface."

Anyway, if it was clear cut, it shouldn't be difficult to get it approved.

These kinds of discussions show why it's a pain to use non standard licenses.