Was he wrong to leave the brownies on the counter?

Was he wrong to leave the brownies on the counter?

"My sister and six year old nephew stopped by as I was getting ready for my old college friends to visit. I had just baked some pot brownies and they were cooling off on my stove. My sister grabbed a brownie while they were waiting and gave it to my nephew. I yelled at her for grabbing one without asking, but she feels like I should have told her what was in them."