So... Greg's currently blowing up on Twitter (and live on the Kinda Funny Games Daily show) about this. He showed a video that proved his badge wasn't confiscated, as he was part of Gamespot's final live segment of E3, where he'd need his badge to get in.
Sounds like a bit of a balls up on the ESA's part here! Options are:
1) Someone copied his badge from a photo from Twitter etc
2) He actually traded it
3) The ESA have made a major balls up
Gonna be a fun ride to watch this one play out!