I agree. Sounds like a combo of sibling jealousy and miscommunication. There was likely something about the plan for transferring ownership of the shoes that your son didn't understand. So he agreed, without out really comprehending what was going to happen next, and when you gave the shoes to the other boy, he felt confused, jealous, even betrayed...in other words very, very upset. This type of thing happens frequently with my own sons (they are twins which also exacerbates jealousy issues). We find that we have to go very slowly, and explain things repeatedly, and really make sure our sons understand each situation.
Having a sense of control is also very important to my sons. Did you take the shoes away to give to Trevor, or was your son able to physically hand them over himself? Allowing my sons to do things themselves, sometimes after a lot of explaining and negotiating even over what apears to be a very "small" issue", helps them to be able to deal with the change.