I saw dancing in the streets among people in the Arab/Muslim world after 9/11. We can debate whether American Muslims were celebrating. But Trump did not fabricate this. Maybe he saw the same news coverage of celebrations in the Middle East that I saw.
I think that's likely what happened. He saw the videos of celebrations in the Middle East, read/heard the reports of celebrations in New Jersey, and now, fifteen years later, he remembers seeing footage of celebrations in New Jersey, even if no such footage exists.
It's not lying, it's how the human brain works. Human memory is not a videotape, and the brain has a way of remembering things in a way that "makes sense."
And, more importantly, it doesn't change the underlying facts: there WERE Muslims, in the United States (and some within miles of the towers) who celebrated the attacks.
Just the New Jersey part.
OTOH, since Palestine doesn't look like Jersey, at all, we all saw the difference and KNEW/remember what's what with this.
I saw enough of the savages celebrating after 9/11 to know that all the pc media manipulation will never convince me they should be welcome in this country.