So here is what I think happened.

Luhan said he was hungry and he's even somewhat his lips.

Xiumin still has those baozi cheeks (man I miss those cheeks)

Luhan being hungry sees Xiumin as an actually baozi and wants to eat him ^^

(( I literally just thought of that when I came upon the picture ^^ so if you get inspired up this *cough* ))

 They're like a couple ^^

Cr of gifs to rightful owner