They've hired several ex-Crytek engineers at the Foundry 42 office in Frankfurt, and among other changes have modified the engine to support a 64 bit data in coordinate system and rendering, multithreaded physics, and independent physics grids for inside the larger ships while they're moving around. Probably other things, but those are the main ones.
Nearly every AAA game is going to fit into that pattern, it's just that the 64 bit coordinates overhaul in Star Citizen is probably a larger and lower level architectural change than what most things bother with.
Well, this is Amazon we are talking about - they like dancing to the beat of their own drum. They also forked Android.