Childermass may not know her personally, but he knows enough about expressions to know that she was caught out by whatever he might have said. He does not wish to do it again, nor does he wish to reveal much more about himself. It's fairly obvious she doesn't want to keep talking to him. And it's just as well he supposes, if she knew who he was.

"You're young, yet, Miss Widdowson," he replies. "You will learn what I mean, in time."

He moves to put his hat back on again, before tipping it at her in turn. "Good day to you, miss."