Because Charles had come from wealth he came with an understanding that thievery was often a sign of desperation, not that there weren't other reasons to steal...there might even be a compelling explanation behind this man's reason. Either way there was no need to bring the authorities into it and the mutant was a very patient soul at the best of times. Even with all of that bearing in mind, he was rather impressed that someone would try to steal from him in broad daylight, indicating that there was at least some confidence and skill behind it.

"I should be relieved that my virtue shall remain intact," he didn't stop walking, but he did close the book...because now he had to know what he was after, or at least why, "so what was it you were hoping to acquire?"