Really, it's only the fact that she'd just been in big, vulnerable tears (and maybe the neck-scrubs too) that prevents him from responding with a skeptical huff of a sigh. He still breathes out a meaningful lungful of air, but it's more long-suffering than dubious. He doesn't want to hurt her feelings.

"It's not worry."

But that is a string of three whole words, so good luck getting him to explain himself beyond that.