I don't put much stock in this analysis either.
I think opinions and attitudes about Trump have been baked in for a long time, and the only factor that gives him any chance at all to win an election at this point, especially after the fit he threw when he lost last time, is the variable created by people who tend to vote Republican no matter how bad the candidate. I think Americans are tired of the lies, the tirades, the name calling, the lack of substance and the crimes, and regardless of the enthusiasm level, Biden was on track for a solid win like he got in 2020. Most of these polls aren't taking into consideration an enthusiasm gap among Republicans that has produced over 20% of a primary vote going to others, even after they've dropped out.
While I agree that this surge of enthusiasm over Harris and Walz should not trigger overconfidence, I don't have much confidence in their analysis. The differences between the two sides in this one are pretty stark and clear. There's not going to be a lot of bouncing back and forth.