He honestly could not tell me why though.
The simple answer is yes, this is typical for a child this age. I actually remember feeling this way as a child, and I was not what anyone would call a behavior problem. I just often couldn't explain why I did a certain thing or why I felt a certain way.
And the pizza and s'mores certainly did not help, I'm sure. He probably was having blood sugar issues.
Try talking to him in the morning. See if he can think back to how he was feeling. You may want to do this after a healthful breakfast, when he is feeling full but not stuffed.
But chances are he never will be able to express exactly what was going on in his mind. I don't think that's something to worry about. But he may be able to help you to work together to find a way for him to unwind (I think of it like a coiled spring) without the tantrums. Children this age are remarkably creative, but he needs guidance to think of a solution when he is calm and away from the situation.
DS '04 "Boogaboo"
DD '08 "Lilybear"