The simple reason is that it depends on what in the floor can't actually handle the 2000 lbs. If it's a floor 1'x1' floor tile that will break, then Elon is right. If the loade limit is a beam that spans a larger distance, then he's totally wrong.

In places like a server room, you typically have a raised floor that supports tiles in the neighborhood of 1.5'-3 feet square. (The raised floor allows for all the cabling and air con to be run around the systems.) If you say that the floor can't support more than 2000lbs that typically means they can't guarantee enough of a safety margin and you run the risk of the object breaking through the floor. Musk's wheel argument is crap unless he can be sure each wheel is not on the same floor support area. (Which obviously he can't.)

However floors the spec will typically have some safety margin and that probably kept him from going through the floor. His logic, while not 100% wrong in the basic statement, lacked a deeper understanding of what was going on and certainly doesn't help the idea that he's a Tony Stark genius. It was a Dunning-Kruger level dumb statement to make.

If this statement was made in isolation I would give him the benefit of the doubt and assume he realized it was a stupid statement once he said it but he just didn't bother to correct himself. However he's made so many dumb and arrogant statements over the past few years, I assume it was just a dumb unsophisticated statement from someone who isn't that bright.