Oh, so now you know the play design?
When Peterman looked towards Clay, he sees the LB dropping in clear hook zone coverage with Clay running straight past him. No DB is anywhere close to make a play on a led pass and the S was cheating towards the opposite side of the field.
In the NFL, sometimes players don't become "wide open" until the ball is thrown. It was clear Clay was going to get WIDE OPEN when Peterman was looking at him, and thus, he missed him.