[krapp]

That would mean they use rockets and jet engines. Which, if we're accepting (for the sake of argument) UFO sightings as evidence, they obviously do not. Naively, and as described, they demonstrate traits which strongly suggest technology far in advance of our own, to the point of harnessing physics we don't even understand.

It would also be very easy to see them coming, because there is no stealth in space and they would need to be burning fuel and giving off heat, and doing so for tens of thousands of years or more.