"Mężczyzna" is a masculine word for the most masculine thing - that is "a man", exactly - but it looks like a feminine word and conjugates like one. But it takes masculine pronouns, adjectives etc., of course.
Well, on a language learning website, proper grammar is sure important ;) But there's nothing wrong with your sentence, apart from the fact that 'this' is your own addition. That's why it was wrong. It should be either "a man" or "the man".