I don't see any evidence that this is fake (CGI and CFD background here with analysis of flow patterns of aircraft in ground effect).
This is a cellphone video with very high compression, but to me the finish on the aircraft looks right, underside has correct lighting, windows are unusual but that's the way they are on a Gulfstream, pilot not blind this is South America, tarmac crew not blind but fully aware, flag does what's it supposed to be the downwash in ground effect would push the air sideways from the centerline which is the direction the flag was already going (and besides there is a huge cardboard that gets blown out from the truck in the correct direction).
The reaction from the guys on the ground is consistent with what's happening, if a tad nonchalant (must not be the first time).
The sound is completely realistic - engine sound, gust sound.
Finally from that position there is 4800 ft runway remaining which is plenty for a G550.
Everything in this video indicates that it is real, I don't see any red flag besides the one that is on the truck.