Well I think we do know because of the mario quote in the post you are responding to. He said:
"We gotta do a better job coaching that, and executing. The tunnel screen bluff by the tight end—I mean, come on man, we’re in Cover 3. You got a flat defender, you got a hook/curl player, and you got a deep thirds guy. That should be a dead play.”
Harris runs straight to that hook/curl point and sits while pointing to the deep third. I think Harris was the hook/curl player and Hill had deep 1/3rd. Right after the play Harris was explaining something to Hill. Def made me believe he was coaching him up a bit. I think Hill's eyes got caught in the backfield and he bit hard on the screen then the TE blew by him when he was flat footed.
Edit: I will say even with Harris having the hook/curl, he likely should not have come crashing down as hard as he did. I think he felt it was a screen as well, got caught looking just like Hill did and was coming flying in to help out the DE Baron who would need to tackle in space if the screen was thrown.