Well, if he was imagining it and pretending he was a duplicate, then he would be able to get all the answers right anyway, and he would be very smart. But yes, Calvin is imaginative. Very much so.
This is a very similar joke to that one Calvin and Hobbes where Calvin teamed up with Hobbes to make a letter to his sick mom saying that Hobbes wanted a can of tuna and Calvin is hungry for dinner.
There’s a theory that it was in his spaghetti and that is the noddle incident. But it’s not true because it happened in school.