When he was in Germany. He was flying around a weather balloon then tried to track this object that from different vantage points looked disc shaped. The guys with the weather balloon also saw something hovering around their balloon and then dart away at 4000 mph.
As soon as I see stuff like that, I immediately know to disregard any figures. Even the most experienced aircrew cannot estimate a distance without having an idea of the size of an object; similarly, you can't estimate a speed when something disappears. If you were flying formation with it, and it pulled away then you can make an estimate based on knowing your speed and the apparent opening rate, but if they say "4000 MPH" then you know it's a figure they pulled out of their arse.
"Truth needs no defence. Nobody - NOBODY - can ever take the footsteps I made on the surface of the Moon away from me." Gene Cernan, Apollo 17