He did everything according to their own rules. No bad faith at all. That they failed to foresee this is their own problem. Things are not as simple as they seem. When people assume they are, they get things like this. They should be happy their gift card offer was accepted and a peaceful outcome was reached. It could have been much worse.

Also, someone was going to win that contest regardless of what he did so it's not like it matters to the pizza place's bottom line.