I was hesitant to bring that up, but yes, maybe.

You do realize that you're the one who's making the biggest fuss about it out of everyone, yes? Vivien pointed out that Jens repeatedly used that term and that he really shouldn't, which I think most people would agree with. You apparently don't, fine. Still, it's a helpful suggestion, precisely *because* English isn't his first language so he probably didn't realize the connotations. I don't see any indication that Vivien or anybody else thought Jens was intentionally rude while using that word.

Your question about why it makes such a difference if it's a noun or an adjective seems fairly silly to me, since you're perfectly well aware of the connotations of the noun. Why do words have connotations - because people get used to hearing them in a certain context, I suppose. And if you object to the connotation and insist on continuing to use the word in the meaning that it should have in your eyes, well, then that's your choice, just as long as you're aware that you'll have to defend that choice on a regular basis. Especially when you're not a member of the concerned group - and even more so if you use the word in a discussion related to the sensitive issue in question. There's not a lot of people who will be giving you the benefit of the doubt under those circumstances.

And for people who don't know the connotation, for instance because they don't speak the language as a native speaker, they may have a good excuse for having used the word, but they should heed the lesson and be careful with it the next time. Happens often enough to me too. Or they can choose to make a point of it and insist on using the word they want to use (like many Europeans do with stubbornly refusing to use the term "soccer", for instance), but then at least they know that this can cause irritation or give offense.