It would be nice if specific offending portions of the codebase were highlighted. As of now, it’s hard to see why one should use this fork. Also, since the source is available, anyone can just compile a past version of vim.

Agreed. Without the context it just feels like a petty reaction. For all the reader knows, it could be completely unrelated to AI. The repository owner could’ve had a falling out with the maintainers regarding features or may be trying to inject their own malicious code into the fork.

A cursory search didn't turn anything up in the vim repo or elsewhere. I can see why the authors of the fork wouldn't want to stir up drama, but I am really curious too.

It’s not about specific offending portions, it’s the principle of having any LLM contributions at all. There’s a group of people who are so opposed to this stuff that they object to its mere presence anywhere.