I find it far more likely that the different interpretations of UFO lead to divergent and self-reenforcing stories. What I mean by that is that UFO means unidentified flying object, which all flying objects, or even just those for which there is only a single report are classified as exactly that unidentified … opposed to identified … flying … objects.

On the flip side, the public that has both a less formal and generally lower understanding of this and other things, also led on by various forms of popular culture, have a wholly fantastical minds image when they hear "UFO".

Seems unlikely that they're participating in a large scale fabrication like this but it's possible. I think it's more likely that there is some black project that uses novel propulsion systems and they're covertly testing it against our own military to evaluate how effective it could be. Or it could be another nation that made a break through in propulsion. And of course, the extraterrestrial possibility.

One thing that will be interesting is to see if any other nations have had encounters like this and can supply video and sensor data evidence.

Yes, this can't be dismissed. (It's also plausible the military could be intentionally deceiving some of its own personnel, for some purpose. So a military pilot recounting a story may not necessarily be lying.)

Obviously such a claim would need evidence and a plausible motive and shouldn't be suspected without evidence; but, also obviously, it's one of many hypotheses that would have a much higher probability of being true than extraterrestrially-originated visitation.

Not saying they aren't, but what possible reason could they have for doing so?