Sometimes Charles knows things because he hears them in his mind whether he's trying to or not, although he seems to have more control over that now. In this case, he knows because Erik told him. He figured he should tell Charles that much, especially when Charles had asked him about staying.

"I'm not leaving right this instant. Of course I would have told you before I left." She and Charles are the ones he'll miss most, after all. They're what he's got for family now. He's not going to ignore that.

"I just can't clear my head with other people around."