ok, I have this play on tape so I might have a disadvantage here
Fact: The slot did not have a whistle on the play.
So if that is indeed his primary why does the lead have a whistle in his secondary when the slot doesn't? Shouldn't an official only go into his/her secondary when the play is obvious and must be called? I'm sure the slot is a qualified official as well, since he was assigned the Duke/Kentucky game. So if, as you say, he had a better look, why shouldn't we trust him to take that play??
One other thing. You are right the block is clean. Just because williams goes down though doesn't mean it was the defenders fault. Wiliams jumped into two guys leading with his shoulder and created all the contact. How can we punish a defender for this? If I'm a college coach and I continue to see plays such as this I just tell my kids to wait until 5 seconds left, drive to the hole out of control, and jump into somebody so we can go to the line.