I'd guess that runoff is a relatively small compared to transpiration. If it takes gallons of water to grow a single almond, there's no way that a significant portion of that is still in the almond when it's exported. IIRC almonds aren't particularly thirsty compared to other nuts, they're just really popular so their stats look the most dramatic.

Indeed, they're not especially thirsty; California just grows an incredible volume of them because we subsidize their production with vastly underpriced water far cheaper than the rate per volume that residential users have to pay.

It takes about a gallon of water to produce an almond, and the residual ends up in the air, where it's basically useless.

I mean, you don't see the state repealing rules about low-flow showers and toilets because "the water stays in California", right?