Someone with more knowledge than I could opine on the range of a G5/6 to determine a possible origin (or refueling stop).
If we accept that, “Flight Tracker” can likely give us an N-number and it’s OFF TO THE [speculation] RACES!
I'm more a spectator on anything but military A/C, but I've dug up the following:
Gulfstreams formerly were labeled as "G" followed by a roman numeral model and those models ended with the Gv = G5 years ago. (Both G"4" and G"5" are shown with max range = 4952nm)
Current production includes:
G500 Range 5200nm
G550 Range 6750nm
G600 Range 6500nm
G650 Range 7000nm
The Air Force C-37A is a milspec G"5" with a quoted max range = 5500nm.
....I don't have an emoji with a raised eyebrow or I'd put one here.