Although confirmed by several 772 Drivers that a fully loaded and fueled 772 would NOT be capable of reaching FL450. Even FL 400 would be challenging at that stage of the flight??
They don't know that. One, the aircraft in question wasn't fully loaded. Two, no 777 pilot has tried to climb to 45000. Their FMS
tells them they can't reach it safely, but that doesn't mean it couldn't have achieved that height if only for a few minutes.