Mettaton has literally no idea what he signed up for there. Such that he flashes his show-stopping smile when Papyrus expresses such excitement. He only stays crouched and petting Papyrus' friends for a short while before straightening up and brushing off his pants.

"Well, now that I've met my handsome new travel partner and his teammates, why don't we finish up shopping~? And I'll tell you what, honey--you can cook tonight, but pick out something different and I'll make it for you next mealtime!!"

He's only too happy to offer an MTT-Brand meal to someone, whether it's just to show off or not!