Was I wrong?

The weather today was very chilly, so I thought it would be nice to stop by Sam's on the way to work and buy some hot cocoa and apple cider for my ociates. I set up the area so that they could serve themselves and provided cups and hot water and called my ociates in one at a time to prepare their drink of choice. One ociate makes a big cup of cocoa and then comes over to my desk asking if he could dump out his cocoa and grab another(because he made the wrong one). I looked at him for a minute and finally told him it was okay to make a new cup, but I made him leave his original cup with me. He asks me why am I keeping the cocoa and I replied that I didn't want it to go to waste. He gets visibly upset and tells me I am "wrong for that" and turns around to leave. I think he over reacted, and I don't understand why. I'm going to talk to him in a minute, but I wanted to ask on Y!A first. Did I do anything wrong?