You must have misread.
EDIT I've oversimplified it, sorry. Actually it IS correct what you just said. Pimax's render distortion engine could choose to oversample in focus area's. We now have the render quality sliding bar in Piplay settings: it's just one setting you choose, but with eye tracking the Pimax distortion render engine could use a higher render value for the in focus parts and a lower value for the parts not in focus.
Yet by far the biggest GPU gain won't be in the render distortion but in the game renderer, so that's why I said that a game needs to support it. Think of the quality setting in games: if a game would support eye tracking, it could choose the focused part with the highest quality settings and the other parts with ultra low quality setting. And that's where the biggest performance gains will be.
So yes, you're right, in theory ALL games can benefit from eye tracking, even if they don't support it, but the biggest performance gains only can only be achieved if a game supports it.