It's the other reason he agrees to have Carl stay; even having been told that the thing from the woods is gone, there's a part of him that's still afraid. That wonders if he's going to go to sleep and when he wakes up he's going to find out that he's lost more time and hurt someone else.

Maybe hurt them even worse this time.

He trusts that those who told him about what had happened were right, that the thing was really gone. But no one said that fear had to be rational.

"You seen Trudy in here since you came in?" he asks, just one more thing making him feel a little guilty about keeping Carl there for the night.