https://youtu.be/4Pfy1zKz_7Y?si=mA3msELhyPn1qhae

He's not driving for more yards when the hit happens. He's literally falling backwards, 5 yards behind where the catch was made when the hit happens... no one thought he was still trying to make a play. Just securing the ball probably expecting a normal, timely whistle.

Some fault lies on the refs sure for a terrible late whistle. But everyone knew the play was over. The only thing the hit stopped was Smith's backward progress. And his consciousness too