My DD has SN and eats sooooo slowly! At nursery she is the last one to finish and the staff will leave her to finish alone, but they are in the room with her clearing up the plates, trolley etc and will watch her and chat to her. She also drops food on the floor which is left until she has finished when they clear her all up (and wipe up the floor too).
So it may or may not mean anything, but if it bothers you you could ask the staff, saying that it ha upset your daughter.