I'm with NOR116.2 's theory, having seen both outboards touch during cross-wind training in the sim - over controlling the ailerons. Windshear at 100ft may well have caused the hard landing, but I'm guessing the aircraft did not touch down 'straight-and-level', otherwise the inboard would not have touched. Obviously very difficult conditions, and one hopes that the crew will undergo further training and then be able to put the incident behind them.