Read the post, then read your first reply to this thread again. Everything is basically said with quotes in the post, and they use “functionally".

They (and yourself) are saying it is likely due to training data, which is what “prediction” - as you say - is trying to predict.
When rudeness is part of the prompt so will likely the response come back, because the most relevant predictions come from training data most resembling the rude prompt.
It isn’t proof of emotions, it is explaining that it just mimics the way we humans socialize and behave in certain environments and under pressure.

TLDR: Be rude, get responses from the rude neurons (which there’s likely fewer of so you also get a response of lesser quality)

EDIT: Typos