They're talking about the speed of the internal engine, not the display. So the display could still only be showing 60 frames to the user each second (or 120, o

They're talking about the speed of the internal engine, not the display. So the display could still only be showing 60 frames to the user each second (or 120, or anything) but the internal engine is running at 6000fps. Plenty (maybe nearly all?) of games do this because modern engines decouple the engine speed from the display speed. In older systems where you knew the engine was only going to run for a specific game on specific hardware (e.g. a SNES or GameCube or PlayStation), and you knew you were always going to be targeting 30fps, no more no less, you could pretty safely assume the game would _always_ run at 30fps and could use a "frame" as a unit of time. So if you want some in-game action like a melee attack to take 1 second, you could just count 30 frames and you would know it was 1 second long. But if somehow this game was later run at 60fps, that same attack would now only take .5 seconds, since there were twice as many frames in a second now. So if you took a game like this meant for 30fps and ran it at 60, everything would just run twice as fast. You wouldn't actually be able to play the original game at anything higher than the original frame rate. What they're saying here is that they decoupled the two, where originally they were coupled. So now the game can run at high fps and feel smoother than the original lower fps rate, but the gameplay is still at the original intended speed.