Is the last sentence from the reference book or is that your own comment?
I went to the Web site of a major Polish newspaper, Rzeczpospolita, rp.pl
I typed in the word "Murzyn" in the search terms. I got a large number of newspaper articles using the word. The word was used inside the body of articles, not just in quotes. This tells me that most people would use it in
the primary sense of a word "Black person"
However, I also found a few articles in how this word could be made offensive in particular sentences/context. So I understand what you mean now. However, neutral words that can be made offensive in particular context also exist in English. I think the problem is that this word has been mistranslated, and there some idiots from Poland who misuse it in an offensive context. However, I would still strongly maintain that primary translation of "Murzyn" is not the offensive "N----r" word in English (if you were to type in the N-word word to search a major English newspaper, would you see it being used by reporters? If the paper is respectable, you would not.)
In any case, I'm not going to fight over this. If someone is not fluent in Polish or grew up speaking Polish or in the Polish culture (this would include some newcomers to Poland like the soccer player mentioned at the beginning of the thread), they will not understand the context of how some words are used. Also, if this word is mistranslated, I could also understand their reaction as well.