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.