Those things partly at play, but I think it's also different at state levels in elections. In national election, everyone will basically vote their party. Every Republican (not every one, of course, but the vast majority) voted for McCain and Romney against Obama, and then for Trump as well last year. Likewise for the Democrats on Obama and Clinton the past 3 elections. The candidates themselves only mattered so much as they could excite their base and get them to come out to vote.
At state-level elections, party affiliation matters a whole lot less. My state has not voted for a Democratic president since 1996 (we're right next to Arkansas, Bill's home state), and before that, not since 1976 with Carter (also a southern governor). But we did just elect a Democrat for the Governor's seat. And one who's clearly Democrat, by his actions. But he had the personality and was more liked overall, so he won. It's much more about the individual themselves in local and state elections, as opposed to federal elections, where the letter beside your name is probably the most important thing.
I think a couple things are going on here. One, this isn't necessarily a new trend. 5 of the last 6 Mass governors have been Republicans going back to 1991. Two, the demographics of NE. Largely, white, middle-class and up, older, and educated. This group isn't tied to one political party via identity politics. They've been splitting their vote for years going back to Reagan or even Nixon's blowout wins. Three, the legislators in these states are overwhelmingly liberal. Electing a moderate Republican (none of these governors are conservatives) to the state house is a great way to check the wild impulses of one-party rule.