All three gear bays feature doors that open (well, hopefully open) only when gear is in transition, though their climb gradient reducing effect on the over-powered collection of spare parts flying in close formation, otherwise known as Q400, is quite negligible. Especially on short leg with 12 pax.
If the final analysis confirms that the cartoon provided by Luxair ıs correct, gear was selected up before rotation and retraction sequence began as soon as weight was off the nose gear. Aeroplane never achieved lift-off attitude (or more precisely: alpha) and just settled on the fuselage.
To say the accident is very interesting is probably an understatement.