I dunno they didnt specify.. They said there was something following the shuttle for the past few days... and nasa was liek bla bla bla blowing the guys in teh shuttle off.. then today they were talking on a via phone or somthing and some shit flew past the window...
Small piece of space junk that may or may not have come from the shuttle. Theyre worried it might follow it in a re-entry and cause damage. Maybe its one of the bolts they "lost" while working on the space station last week.
The piece that they THINK fell off was in orbate BEHIND the shuttle but on the same orbit. The shuttle was traveling much faster... so they'd have to loop the earth a few times to lap the debris