The screen is a great call against teams that tend to focus on "getting after the QB". I heard Bill Parcells say once that he liked to call screens and draws to slow the pass rush down. That first screen by the Cards worked great because the Bills' pass rushers were keyed on getting after Murray, and I wouldn't doubt that play made them hesitant going forward (especially in the first half).
As for "defending the screen", I think it's more about recognition which comes with either experience, or a D coordinator literally telling his D to be aware of it in a particular situation. But, hey, that's just my opinion man....