(Not a lawyer either but—)

The original author said they were “the license holder”, specifically with a “the”, in discussions around both Starlette and MkDocs, which yes, just isn’t true even after rounding the phrase to the nearest meaningful, “the copyright holder”. This appears to be an honest misconception of theirs, so, not the end of the world, except they seem to be failing at communication hard enough to not realize they might be wrong to begin with.

Note though that with respect to Starlette this ended up being essentially a (successful and by all appearances not intentionally hostile?) project takeover, so the emotional weight of the drama should be measured with respect to that, not just an additional copyright line.