I'm not sure people saying this know that the author is one of the "core developers" of Django. It is safe to assume that his expectation of "open source" is not far-fetched at all.

While you may have a point, language developed with closed process and just the source published in one of the famous code hosting sites need not emphasize on having a "community"[0] if it is not really looking to hear things from the "community".

[0] - https://elm-lang.org/community

The terminology is irrelevant. If you have certain expectations from the open source communities (among the diversity of possibilities that are open source) the narrative of what happened (especially with regards to being considered persona non grata if you fork) are worth knowing about.