I love the feeling I get when someone is hitting on my wife and she responds to the guy no matter how subtle she might be about it, and it sounds as if your wife was responding to the guy going by the reception you got when you started talking to her about it when you were in bed and her response with the wonderful sex you had.
Even though my wife has fucked with a lot of guys over the years I still get that �gut wrenching feeling� when I don�t know what is going on for sure, and even sometimes when I see her responding to a good fucking with another guy and she goes right over the top with him (I have often thought will she ever be satisfied with me again).
I think there is a pretty fair chance that something might have happened between them, �maybe in the shower�, what is her background with other guys, had she been with other guys before you? Have you ever talked to her about swinging and swapping?
I know with my wife if we start talking about other guys she has been with while we are fucking she wets right up and puts more into it, but then if your wife has had no experience with other guys at all just being alone with him might have been erotic enough to turn her on, who knows?