A trained pilot is still a normal human. It could be lies, exaggerations, misunderstandings or any mixture of things like that. It could be a thing they made up and decided to fool a lot of people with, for whatever reason. Or it could be one guy seeing something, exaggerating what he saw, then another person wanting to be part of it and exaggerating it a bit further. Maybe trying to cash in on it, or just trying to become famous, or just trying to feel life's more exciting, or just telling a lie/exaggeration to have people believe in what you believe in even if your evidence for it wasn't true. Like, lying for a "good cause", like what a religious person could do (believing in angels, claiming you saw an angel even though you didn't but it doesn't matter to you as you believe in angels and for you it's merely just a white lie to make people believe in what you think is the truth).
There are a lot of people in the world who willingly take part in all kinds of scams (demon exorcisms, having people fall by touching on the forehead at some churches, healing a person by pretending you push your hands inside a person and take that person's organs out, all kinds of things), and a lot of people are willing to exaggerate what they saw to make it feel more believable or more exciting or whatever.
And it's not the entire planet. Just a very small portion of people who make these claims.
I'm not saying they definitely are lying or even exaggerating, and I'm open to the idea that it really was alien stuff they told about, but I'm just saying that it's well in the realm of possibilities that four highly trained people fully or partly made things up. If we are willling to believe that people with certain status wouldn't lie, then to me that only makes it more probable that someone eventually would use their status to make a lie more believable.