Maybe he became friends with Chomper, who showed him stuff that he eats while in the great valley. Someone else can do Chomper, or I can if no one else wants to.
That is just one option, if you want to say your char has already been there a while. After all they put Chomper in, poof, with no explaination of how the grownups came to accept and trust him around their kids, so if it's good enough for a feature character, why not yours, though that is up to the GM if he'd allow such a thing like this.
There are other options also.