macrocephalopod

if you update delta when spot moves, then spot lower => nope lower and spot higher => nope higher, right? hence “it’s a measure of intraday price movement”

Not particularly, no. There's some tracking sure for options closely near the strike and on opex days, but in general NOPE's movement is largely dictated by incoming trades, which do not move in such a linear way.

It'd be a bit silly to think that the net delta each day is being set by how the spot moves, and we have fairly ample existing data + observational data to reject that.

Well I think the is a proportional relationship between delta and spot, so there should always be a high correlation between deltaNope and deltaPrice. That is where price tracking occurs, however the raw Nope value, sometimes diverges from the price movement or can lead/lag

My only claim is that the main thing causing nope to move up and down is the stock price. The option flows are a second-order effect.

Oh, I have no idea if there's causation here, but all I know so far is: - yes there is correlation - yes it does generate alpha forward and backward - yes it seems to imply what's predicted in the reversion hypothesis (higher chance of reversion at higher NOPE magnitude)

You could potentially argue that delta is flowing due to the stock price moving, but that doesn't really impact the underlying reversion hypothesis. NOPE is clearly not measuring SPY price moving.