I have some guesses:
- The cinema was closed in the afternoon
- When she left she had no coat and came back with one
- She had some of the clothes messed up or different from before when she came back (Or maybe the shirt inside out)
EDIT:
Since he was looking her walking to the door, it might also be something noticeable only from behind (hair?, hook closure of the bra?, socks? )
RE: Daily Brain Games (Nov 13) - how witty are you?