Hermione could always appreciate someone who could laugh at himself, if only because she had a difficult time of doing the same. It showed a sort of self-confidence that she just didn't have, and so seeing it in others was heartening, in its own way.

"I wouldn't call it foolish. After all, you just want to make sure that I get good enough not to shoot you next time. That sounds perfectly reasonable to me."

She didn't know if she'd consider it "the nature of her heart" so much as it was simple common sense, but that just showed the differences in their general outlook.