Iowa had its primary in June, and the Democrats did not have much for contested races (other than 1 of the 4 congressional seats, and then a smattering of state house/senate seats) I'm speculating the big shift to R was due to more contested primary races and people registering to vote in them. And especially in western Iowa, the R primary is THE race. Even if they have a D opponent, the final winner is coming out of the R primary.
So my point is, while it is nice Iowa had a huge shift, is is more a function of June being primary month.