Kießling followed the ball and threw up his hands in horror and directly realized that it didn’t go in. When Brych later confronted him he didn’t admit it.

it looked like he told the referee

We don’t know what he told the ref.

Seems pretty unlikely he’d be sure enough to say for sure that wasn’t a goal. He looks away from the ball right as it hits the side netting, and then he looks really confused that everyone else thinks it was a goal. Kind of hard to be sure of anything there.