This is a 200, not a 100.
I doubt anyone tried to retract the landing gear. The logic would unlikely have allowed it. My best guess is that when the nose penetrated the brick wall, it wiped the nose gear off and the six attachments in the wing box sheared and the fuselage rolled over the wing box, centre fuel tank and landing gear wheel wells. This aeroplane is a write off. But, modest negotiation with LH Technik should shore up Rwandair's CRJ spares.
If there was uncommanded thrust in the right engine (btw, there are no throttles in a CRJ) looking at a building 500m away, a push of the R FIRE Push switch would have reduced the thrust to zero. Plus, the full application of brakes might have then made the difference with about 100m to spare.