He doesn't lean back. He very deliberately does not lean back.

"I might ask you the same question," he points out instead. "I'm not the one following people - though I guess that's not the right word, is it? Preceding, that's the one." If nothing else, this unwanted proximity has given him plenty of time to listen. The more he thinks about it, the more different she sounds from the way he remembers. That was only a week or so ago; what could possibly have happened in such little time?