Watching that video, it looks like a large chunk hit the upper part of the leading edge of the wing but then was sucked below the wing (I saw no debris fall along the top of the wing, but a distinct splash on the underside of the wing). It seems strange that something that struck the upper portion of the leading edge of the wing would then be sucked below the wing, because a wing creates an area of low pressure on top of the wing. At least that is what a normal wing of an aircraft in normal flight does. I have no idea what the aerodynamics are of a shuttle wing during liftoff.
At any rate, watching the video, it sure looks like the object impacted the top part of the leading edge, but then was sucked below the wing.