I can't say whether the original spec was written with AI assistance, but having a cursory look through the commit history [0] it doesn't look like they're just blatantly auto-generating the docs. The git history indicates that they do think about the spec and manually update the docs as the spec changes.
I don't write perfect English. Far from it. But I'd prefer broken English any day over default LLM verbiage. It seems so unnatural and facetitious. I always have this in my prompts: "Be succinct and use simple English sentences".
[0] https://github.com/modelcontextprotocol/modelcontextprotocol...