Having spent some time hovering over large built up areas at night I do not believe that surface definition is that difficult from the air. There is usually sufficient environmental lighting for the buildings to stand out and ground features easily recognised. This building had lighting all around and would have been easily identified from the air.
The AAIB report states the aircraft struck the building with the blades not rotating. It cannot therefore have arrived "in flight". In addition, loss of hydraulic power at the bottom of the NR range would have simply compounded the pilots attempts at controlled flight.
This was a "crash" in the traditional sense. Arriving at an undetermined point with no control at all. Sadly!!
The AAIB report, as I read, infers the Fenestron was still able to be turned by the No 2 engine FPT accepting however that the Fenestron detached during the crash sequence. I think this rules out Fenestron related theories!!
DB