I’m a native speaker and interpret “man” in this context as definitely male, and I’d be very surprised if any other native speakers disagreed with that.

I think it’s because “a good man” is quantified by the indefinite article “a”. Whereas “man” in a sentence without that qualification, e.g. “one small step for man” I would not interpret the same way. So, “a man” = a male human, “man” = maybe a male human, maybe any human.