While I have written that comment somewhat quickly, that's not AI at all, I can assure you about that. :)
For instance, if I followed the principles of indignation culture, I could be offended by your "I can assure you about that :)" statement. I could say "Are you making fun of me?!?!"
To be clear, your statement is perfectly fine. I understand what you're saying, despite disagreeing.
Also, this happened in an English language forum. It's reasonable to expect that foreign speakers would be somewhat versed in the conventions of the English language and see that the comment was not offensive at all.
Some cultures value relational power in leadership, and so their language reflects preserving relationships as a base resources. Some cultures value authority, and so their idea of being polite might involve some maintenance of authority at the expense of perceived care or relationship.
I'm just saying the words that convey rudeness are not necessarily just a superficial dressing on the same thing. Politeness is a shorthand that is also about alignment with a cultural value. Cultural values differ. My being annoyed at someone else's cultural posturing as default, that's not just mindless indignation. Values matter.
It's of course impossible to say if this was just an unfortunate choice of phrasing or if it's a sign that Mozilla has become that soulless corporate entity (I say this as a Firefox user for more than 20 years).