My daughter doesn't necessarily do that, but she has been being weird about food. Not eating much, throwing it on the floor ect. I'm assuming its a phase.

My son will do that when he puts too much in his mouth

My daughter started doing that around her first bday, and she still does it all the time. First I thought it was because she had too much food in her mouth but now I just think its when she's done eating that. Because if I try to give her another bite of it she turns her said and says no. But she will accept other food. So just make sure he has a few different things on his plate, and remember their stomachs are only about the size of their fists so if he refuses to eat as much as he did before he will be fine they only eat when they are hungry ☺️