I think there are not only difficulties in understanding US law but specific state provisions.
FWIW, there are Californians on Twitter saying that the bathroom laws do not cover changing areas or specifically female spaces like this when there is a choice - bathroom laws include that they can only be mixed when there are privacy stalls.
From what the young woman in this video is saying about the transgressor with legs akimbo, that instance is not covered.
However, that's Twitter, and there must be some nuance in play - presumably around the legality of asking someone to validate their status irrespective of provisions.
I am so angry that low wage, minimum protection women like the manager are being put up front to defend this. Legislators everywhere have put women in these invidious positions and have done it knowingly, hoping soft words turn away wrath even when that wrath is righteous.