Angels, ghosts, UFOs, miracles all have the same characteristics. A person who seems very reasonable says they are sure that saw the thing, and they provide SOME circumstantial or grainy photographic evidence, but no one actually got a full resolution picture of the angel or ghost or UFO.
I doubt these people are lying. They actually saw something. Miracles are the easiest example to explain. Someone couldn't walk and then a saint said a prayer for them and they could walk again. It is pretty easy guess that it was a placebo effect or coincidence that the medical issue got better at the same time.
We have never seen someone with a X-Ray of a severed spine regain full walking ability after a prayer from a saint.
UFO's may exist, but it seems more likely that a combination of reflections, radar issues, tiredness/stress, "wanting to believe" caused them to see "something"