It's a holographic projection into the upper atmoplane.
Holographic projections are transmission images. That is you have to see the film that the hologram is stored on to be able to see the hologram. This means that they would need massive hologram projectors up in the sky, and these would be visible. As they haven't been seen, then it appears that they don't really exist.
I, personally, have made holograms. They are not that hard to make. They hardest thing about them is making sure that there is no movement of the object, laser or film while the exposure is being done.
Also, you can't project holograms onto a "Screen" like you can a 2D image as the holograms need to reconstruct the interference pattern on the film for you to be able to see them. Reflecting something like that off "clouds" or the like will scramble these interference patterns and spoil the hologram image for the viewer.
So, no. It can not be a holographic projection because holograms doe not work like that (well they do in sci-fi, but that is sci-fi and not reality).