Sure, if they have some bullshit antimatter technology figured out. But I personally find it hard to believe that there would be any other civilizations close to Earth, so I have no idea where they would be coming from. Or I guess if they can manipulate their speed like that, distance isn't a very big problem anymore, so I guess at that point they could just as easily be from the other side of the galaxy
All I know is that my brother saw a weird light accelerate into the sky at ridiculous speeds one time. If you've seen that "Jerusalem UFO" video, he says it looked just like that. He saw a light hovering in the sky and he asked his colleague if he sees it, they were confused about it for a second and then it just shot up. So I'm inclined to believe that people really do see stuff like this, but I have no opinion on what they're meant to be
