One thing that strikes me as odd is the relatively little yaw the aircraft was subjected to after the collision. It struck the building with its outermost wingtip at taxi speed and sliced into it substantially, but during all this it apparently stayed pretty much aligned with the taxiway instead of being swung around by the long lever arm and taking a right turn onto the grass.
This is most likely a testament towards the buildings relative structural weakness; it does seem to point to a low (-ish) taxi speed though.