As much as I REALLY want to see them smoulder each other with kisses, that gif doesn’t really seem like as though they were kissing. I’ll just point out how it seems like as though Xiumin was checking Luhan’s body temperature by comparing their body heats. Besides, I don’t think they’d dare to commit such things in public.
Xiumin was also wearing a face mask, so that makes sense. Maybe he wasn’t feeling well and just needed a hug??