Something similar happened a couple years ago involving photos being taken of employees.[1][2] What struck me as different this time was that neither the FA nor the GS Rep attempted to take the camera away or have the pictures deleted. If this was a security issue, it makes sense that they wouldn't just let him walk off the plane with the photo(s).

It's possible that his saying "terrorist" was part of it, or maybe UA has a very strict no-photos policy, or maybe there's something else we don't know (and I think this is probably the case,) but this still seems pretty absurd.

1: http://consumerist.com/2011/07/28/united-says-photographing-...

2: http://consumerist.com/2011/04/25/allegations-of-photography...