Except, it isn’t actually the Pizza Planet truck, as the company is actually called Pizza Realm in the world of this movie.
Simply enough, since Onward is fairly modern movie all things considered, getting the Pizza Planet truck into Onward was easy, cars and trucks are normal things here, and so that’s what happens.
When you see Barley and Ian paying their toll at the “troll bridge” (seriously they shove like four gags into one moment here) look off to one side and you’ll see the Pizza Planet truck.