The shuttle may have been moving in excess of 1000 mph, but remember the "brick" started out moving at the same speed. The actual relative speed between the two would actually be very small. The "brick" stopped accelerating when it broke off and only traveled a small distance before hitting the wing.
now... that was a good sized chunk of whatever it was... and i would guess it would accelerate to some substantial velocity with a 2000 mph wind on it in 40 meters, then striking a body traveling in the opposite direction... the relative difference in velocities could be significant.
momentum... mass (we don't know) X velocity (we don't know).
but... my guess is that even a couple pounds of whatever it was, would be cranking with whatever mass it had... and very well could have raised some serious havoc.
i've seen 200 mph winds stuff a 2X4 through a car.