Mario shakes his head at BJ... basically telling BJ that he is WRONG.
Mario never called it over at sound of the horn.
He let it continue even after Sherk got rocked by the knee.
At the left of the camera shot you can see Mario walk to Sherks corner... going to check if Sherk can answer the bell.
By this time, Sherks camp is already working on him.
You can see Sherks corner guy getting him ready, the bout was NOT over yet.
So if Sherk was really OK... he would have be able to show Mario right then.
Clearly this was NOT the case.
He called the bout after checking Sherk out.