Just to add to it, a Shahzada, that is a Prince, also comes from the same suffix, as he is son of a Shah, a king.
But somehow, looking at posters of the movie, I get a feel that the director here wants to say that Ishaqzaada is someone who is too much into love, to an extreme. That the world calls those lovers ishaqzaade as a swear word, just like Ha**mzaade.
That is what seems to be the story to me. Would still like to know what is Habib's explanation though.