PR was rejected because of this. Agent then threw a fit.
Now. The only way your defense of the AI behaviour and the condemnation of the human behaviour here makes sense, is if (1) you believe that in the future humans and healthy open source communities will not be necessary for the advancement of software ecosystems (2) you believe that at this moment humans are not necessary to advance the matplotlib library.
The maintainers of matplotlib do not think that this is/will be the case. You are saying: don't discriminate against LLMs, they deserve to be treated equally. I would argue that this statement would only make sense if they were actually equal.
But let's go with it and treat the LLM as an equal. If that is their reaction to a rejection of a small PR, going into a full smear campaign and firing on all cannons, instead of searching more personal and discrete solutions, then I would argue that it was the right choice to not want such a drama queen as a contributor.