On average, the D less R margin in the early vote mispredicted the final Clinton/Trump margin by 14 points! Pollsters get yelled at when their polls are off by even 3 points, and anything more than that is considered an absolute disaster. Imagine if a poll was off by 14 points: no one would ever listen to it again! And yet we get the same frankly amateurish analysis of the early vote in every election.
He literally talks about that at several points. 2020 is a horrible baseline for looking at anything analytically because it was such an outlier because of COVID. Too many other variables in 2020 for it to be applicable for anything