Yes, she has almost certainly had a bit of a fright outside. Maybe being beaten up by another cat, or a horrible human giving her a kick (which happened to our Basilcat - he won't have anything to do with men now apart from Mr Frog), or even something like roadworks happening in her usual territory. As long as her eyes are still bright and she's looking after herself, she should be OK, but as others have said, keep an eye on her over the next few days just in case she's poorly. (And I know exactly what you mean about her not being able to say what's wrong!)