Then you’re wrong I’m afraid. How did you get that impression?
It is a theorem about how far back you can extend the dimension of time, it doesn’t say anything about whether it is coherent to speak about a “before” time itself or what there might have been, or even if the universe really came out of nothingness. It just doesn’t say that.
Apologists who rely on it in debates usually invoke the BGV theorem as an argument against theories that postulate an infinitely old universe. But again, saying that time has a first moment a finite time ago, is different from saying that there was nothingness before time itself and that the universe literally once never even existed. There is no evidence that the universe was ever somehow not in existence.