I don't believe it!
I agree with Wes Wall and Rollingthunder.
Lets say the Shuttle is travelling at 500mph. That means ALL parts are travelling at 500mph.
Now if something falls off, it slows down due to drag, but still has less (and getting lesser) forward momentum. So how much did it slow down in the distance between the falling off point and the point at which the orbiter LE caught up with it?
I would hazard a guess that it was A LOT LESS than 500 mph relative speed.
Think about it, you're overtaking another car. Its doing 80, youre doing 90. Takes a (pucker factor) while doesn't it?
I smell a cover up though of what, Bad inspection, missed damage etc, I dont know.
But I do not believe the foam was travelling at 500 relative to the wing. I DO believe that there was damage to the LE whether pre-existing and made worse by a thump from soggy foam or a tile just waiting to fail.