Yes, it's unfortunate that the flight attendant lied in this situation.
However, it would have been impossible for the pilot to verify this - even if the author showed him the camera. Since the author was willing to 'prove' it, it had to be a digital camera - which the author could have very easily used the built-in delete function to remove all photos but one (or be a sneaky terrorist and swap SD cards).
In addition, the author made the statement "I am not a terrorist." There's no way for flight crew to know this to be true until the plane lands at its destination and you provably haven't blown it up, killed people on-board, or hijacked and redirected it to another location. There is absolutely zero value in making a declaration like that.
... In fact, I'd say there's negative value in making that statement. In a security conscious environment like an enclosed aircraft, it immediately escalates a situation from "photo-happy tourist or possible bad guy" to "higher probability bad guy or maybe making a political statement ... or just not very smart". It's also a (very small) step in the direction of yelling "Fire!" in a crowded theater as you've potentially now caused (possibly over-sensitive) people hearing this statement to begin to have concerns about you and their flight. You've turned what should have been an uneventful flight into a situation where tension can only increase before you've even left the ground.
When you add all of this up, especially when a flight is trying to get out of the gate on time, the pilot is going to err on the side of caution and kick you off the plane.
You'll either blow up in a rage of righteous fury (thus proving to all that you should never have been on that plane) or you'll leave quietly, a one-time mistake, and board another flight (hopefully with much less bother to the next crew considering how much time you just wasted).
You were not kicked off for taking pictures. You were kicked off for acting odd.