Think back to your junior high days. Every teacher was different with the rules. In some classes you could eat and drink to your heart's content. Then there were those other classes where the teacher wouldn't even let you chew gum! And of course there's always that one teacher who will let you eat, but there are a lot of rules written around it, almost in an effort to to prevent you from eating in class.
In this case, we have a teacher who told her students they could have fruit in class. Now, here's the deal, she didn't specify what fruits were acceptable. Sooooooooooo, one of her students took advantage of the situation and brought in a watermelon!
Hahahahahaha! Dude even brought a cutting board! Brilliant!