He's a New York businessman -- 90% of the people he deals with (his banker, his lawyer, his managers, etc.) are Jewish. This is confirmed in his own book, The Art of the Deal, which was also ghost-written by a Jewish guy.
Also, his daughter converted to Judaism.
Furthermore, he's demonstrated his disdain for Muslims very publicly.
So what the hell do you expect? He's still the best candidate out there by far.