I was thinking he may have mixed it up as well. If my snake rejects the hopper I'm going to try a crawler rat next.
On that note, do you think the store would take the hopper back? I was able to return a mouse before, but that was only because it happened to be pregnant and ended up giving birth before I could feed it to my snake. There's nothing wrong with the hopper and if my snake eats the rat crawler I'm not sure what I should do with the mouse, as I wouldn't want to keep it.