The Redskins have three starters on the offensive line who are dealing with knee injuries(LT Trent Williams, RT Morgan Moses, and RG Brandon Scherff). Scherff went down with a knee injury on the Redskins last offensive series. Scherff has been wearing a brace for weeks, so any injury is going to get extra attention from the Redskins medical staff. Scherff limped off the field and was evaluated for a knee injury. He is a tough SOB and has now returned to the game.
Smith was either looking further down the field, or not expecting Reed to break out, because he had him there and wasn't ready for it.