"I wouldn't say I got into a mess," Mettaton admits honestly. "The mess was on Alphys' shoulders, I gained fame!!"

He almost sounds proud, until he realizes he's caught out on being dishonest, so he shouldn't be acting as if he wasn't in trouble. That said, he does glance at Toriel in surprise. The fact that she deems it his business to tell anyone else that he's a ghost...is both a relief and also quite kind of her.

"I appreciate you FOR THAT, darling. I hate to admit that I'm in any way imperfect, but the fact is that I don't believe I'm ready to tell anyone about this.

I'm still sorry for lying to you though."