It seems that the Grindhouse event is genuine and 4 faux trailers were made, one by Edgar Wright (Hot Fuzz) which was made apparently in only 6 days. In a recent interview, Edgar was reluctant to confirm who was in the trailer.
"Completing the trailer literally right after he wrapped up shooting on "Hot Fuzz", Wright had to shoot, edit, grade, mix, etc. and deliver the trailer all in the space of six days. He managed to rope in some big stars apparently to appear in his trailer, but won't reveal who and is keeping it all a surprise."
At this time we have seen no other mention of Matthew's name but Rafe Spall was mentioned in a blog comment from someone who had seen the trailer.
Another article from here talks about the trailer called Don't or Don't Scream, which will be shown on April 6th but again no mention of any stars.
