I don't want to make too much a not very important flub (whether he believed it to be factually true or not), but I do find too many Americans, both those who don't travel and those for whom traveling is just going from resort to resort - golf course to golf course - have no good sense of the scale of other countries. They're real places. Even Yurp is a bit "different," and not just because of those no-go zones. Lots of people living their lives.
Belgium's about the size of Maine.
That's a big city!
While bringing up recent terror attacks in Europe, Trump stated that “Belgium is a beautiful city.” He almost certainly meant the capital, Brussels.