The onboard data recording doesn't show (to us) brake pressure, merely brakes on or off. It's never shown how a driver uses the brakes, only when he does so.
He obviously hit the brake pedal, but caught some of the throttle with his foot, which pressed it a bit (but not 100%). He probably wasn't in a condition to allow him more accurate control of his feet.
As he hits the wall, and breaks the brake lines, the pressure falls away to nothing and the light goes off. The pedal will then go to the floor, allowing his foot (which I guess is pressing like mad because of the pain (and maybe brain injuries causing his leg to spasm a bit, but I hope not)) to fully press the throttle.
I've seen the pictures and videos, and I hope that he's okay soon. James Allen is saying (on twitter) not to pay attention to the Sky News story about him being in a life threatening condition, which I suppose is a good thing.