It looks like a rain drop on the windscreen that is being illuminated, when the car moves it is no longer illuminated and fades out. Either that or
just a reflection as others have said.
What ever way you look at it, another 'UFO' / red reflection appears above the truck that is in the film 10 secs. It just happens to be above the
trucks top right (red) light.
If you think the first light was a UFO, then this one must also be one...or maybe just another reflection.
I don't believe, as a reflection, this follows the rules of refraction and reflection. At no point does it bend how I expect, and even then ... its
movement is very eratic for a stationary vehicle allegedly reflecting a light from a slow moving vehicle. Also, I don't see any reason why this
reflection would be rotating. Reflections tend to ease in and ease out in many cases, especially on curved surfaces. This is sort of lazily moving at
a consistent rate.
Some examples of car window reflections:
The youtube user 'ufoshack' has a number of easy to question videos on their channel all of a similar nature, and doesn't seem amazingly interested
in the results of the discussion on their videos. The video itself is quite conveniant. There's no panning to follow the object in question, it
quickly ends ... The size and speed of the object concerned would be quite elaborate if it was an alien craft at the implied distances. The
description is vague and unhelpful. It doesn't pass a number of spot tests. Possible conclusions:
1. It's fake, and a good example of basic image editing. The ufoshack user likes getting more hits, and has adverts on their youtube channel.
2. It's a fairly giant alien craft that moves like an awkward animation at a very consistent rate and spins, and no one noticed it.
3. It's an incredibly special spinning reflection that moves like nothing we've never seen, and moves like an awkward animation at a constant rate
and doesn't bend/warp despite movement.