Give it a try.

How did your friends know they caused the aggression and the snakes were not just aggressive?

I handle my snakes on a regular basis and you can see my collection below. Its a good bunch of eaters but I have never been tagged being mistaken for food.

I have even accidentally held my hand in front of my ball in its cool hide when I thought it was in its warm one. As soon as I realized where she was I brought the rat in front and she hit it right away. She knew the difference. I think they are smarter than they are given credit.