Do you scrap food off babies chin?

My dietician said not to scrap food off my sons chin while I’m feeding him because it’s annoying for babies and can be a problem for their sensory (something along the lines), so I stopped. This morning my mum offered to feed him so I could have breakfast and I noticed after every spoon, she would scrap his chin, even when there was nothing there. I said “mum you don’t have to scrap it everytime”. She said “don’t listen to those people, I’m cleaning him”. I said “okay, but he has nothing on his chin to clean”, to which she said “leave me alone, I’m feeding him so I will clean him”. I just left it because I’m not going to start an argument first thing in the morning.