I think it's pretty clear that the makers of the game treated JJ Abrams' Star Trek as a full-on reboot, rather than the branching timeline that the movie writers have claimed in interviews.
That said, the radically different Gorn types don't bother me - different castes have been a staple of the novelverse for years now. The Gorn Champion is likely the game's visually upgraded version of the Bad Rubber Suit Gorn from "Arena" which in the novelverse is the Gorn Warrior caste.
The backstory is more difficult. I think it's a poor fit even for the very little we know of the Gorn in Trek canon. But the same could be (and was) said about the Klingons in The Motion Picture and beyond - they were completely changed simply because Gene Roddenberry wanted to.
And I like BillJ
's idea of an Vulcan/Romulan-style ancient cultural schizm.