I figured that they probably couldn't dock at the ISS, but it was just a thought. I find it hard to believe that insulation from the tank could've caused damage. Unless, the insulation that they are talking about is a hard insulation. When I think insulation, I'm thinking styrofoam type or something pliable, but I don't know much about it.
To me, it looked like a piece of ice that hit the wing, not insulation. If it were ice, it could most probably damage the tiles.
>>...I find it hard to believe that insulation from the tank could've caused damage...<<
The vehicle was moving at Mach 2 to Mach 4 so the insulation hit the vehicle at that speed. The tiles are very delicate.