as a mother, i would have taken a strip off him from top to toe.
it is OK to stop others' children from doing something that could be dangerous or something like that, but if he had yelled at my child, there would have been no stopping him.
once at a shop that was filled with kids' stuff, my helper took my daughter in to buy something. my daughter was looking at the cards on one of the spinning displays. the store clerk yelled at my daughter. my helper got mad at the clerk. then she told me what happened and i went in with guns blazing. it wasn't like my daughter was running around the shop pulling things off the shelf, even is she had been, a nice, "excuse me, sweetheart, please don't do that, something might break." would have been more appropriate than screaming at a 2.5 year old. needless to say, we have NOT been back to that shop and never will go there again.