Trump is a regular guy. If Trump said that, and there is no reason he shouldn’t have, he could have had any of a number of reasons, including just joking around, pretending to be a parent telling a kid to eat his salad, or perhaps himself not knowing what other smalltalk to make at that point in the dinner and landing on a lighthearted, ironic comment. The press doesn’t know how to handle a real person. I presume someone overheard this and scraping the bottom of the barrel for something negative to say tried to make a mountain out of a trivial remark.
That's exactly how I read it as well. Probably just joking around.