The G stands for Grubee, as in Don Grube.
https://grubee.net/pages/about-us
Just like the Skyhawk and GT5 references that are the standard of quality, outfits that run under names like gasbike and kings simply build cheap knock off's and try to use a recognized good products name and numbering.
Heck, it's even going on with the gas tank frames.
If it's any clue as to whats real, gasbike/kings and some other names can't even buy real Skyhawk or Grubee anything, so no matter what the ad says, it ain't quality, they have never been about quality, just easy money from suckers to pad their bank accounts.