This. Dupree pushed the tackle deep into the backfield and forced the play back inside, which is a significant part of "sealing the edge." I agree that Dupress was a bit too deep when he did so, however. But the reason why we want that OLB to seal the edge and force running backs inside is that the pursuit should be there to wallop him.
Neither ILB was there, no S, so he had room to scamper.
Watt is already looking in the backfield while engaged and he's only 4 games old. Dupree needs to do the same. With his size advantage, he can always shed and tackle paired with his vision.