That line only leads to a repetition of moves if it's played as a joke by mutual consensus. It's sort of like two people pointing guns at each other verbally accepting to drop their weapons. Will one of them hold on to theirs?

I don't understand how proven is the right word here.

Only if Leela etc decide with high confidence that that line is the best possible for both players would I start to believe it.

I like this human forum, I mean, forum.