If the AC had remained in Flare mode a pitch down order would be introduced and the behaviour and feel of the flight controls would be very different to what a trainee would be used to. Any release of the side stick, before flight mode has resumed, would mean an immediate pitch down. This would be compounded if the attitude at 50`on the approach was very nose down, as that is the reference point the system uses for the flare manoeuvre.
An unstable approach path with a steep nose down attitude crossing 50´followed by a hard landing with a failure of the air ground sensing logic would have prevent the aircraft flight control laws transitioning to ground mode. At "rotate" the trainee would have pulled the side stick to start the rotation, if he then released the pitch input on the side stick (as in a normal T/O) the aircraft would have pitched down and maybe made contact with the runway. If we combine this with an over-keen "positive climb - gear up" call the aircraft might have contacted the runway with the gear in transit. Leading to damage of the gear doors and engine contact with the ground.