Criminal intent is defined as the resolve or determination with which a person acts to commit a crime. It is not defined as ..."Resolve or determination with which a person acts to commit what he thinks is a crime".
Here's a simple example: You see what appears to be an unattended lunch truck with a tray of sandwiches just sitting there. You grab for a sandwich but drop it. Crime of intent or not? Additional fact: sign at the front of the truck, "Free sandwiches" Still a crime of intent? Nope.