The remarkable aspect of Trump's people "cheering on 9/11 in Jersey City" thing is being missed:

Trump has a number of interesting sources of "information", and he seems to have adapted this little fun fact from something else.

There is no question that Trump gets fed a lot of conspiracy nonsense from the internet, through whatever channel he trusts. For example, he was certainly up to date on various aspects of Obama birtherism, including the "forged birth certificate" claims that circulate in the internet fever swamps.

Then, there are the "crime statistics" originally sourced from a neo-nazi website, which he tweeted this weekend.

His identification of "Jersey City" as the location of people allegedly celebrating the 9/11 attacks is actually more revealing of where he gets his information, since it is one of the variants of the "five dancing Jews" 9/11 myth:

http://www.911myths.com/index.php/Dancing_Israelis

"Witnesses saw them jumping for joy in Liberty State Park after the initial impact (5). Later on, other witnesses saw them celebrating on a roof in Weehawken, and still more witnesses later saw them celebrating with high fives in a Jersey City parking lot."

It's of passing interest that he seems to have pulled this story, with a change from "Jews" to "Muslims", out of the same well of internet conspiracy theories where he tends to get most of his other "information".