I don't think you can discount the populations of elderly Democratic voters in these New England rural areas. People that have been voting Democrat since Kennedy or longer.
Maine tilted pretty hard, with the rural 2nd District going convincingly for Trump. However, LePage also gets a lot of support and approval from those same regions, even now, with everything he's said and done, so we may just like blowhards.
I'm not discounting anything just saying the map the author used as proof of his or her hypothesis doesn't follow for the Northeast of the US from first glance. The thing that really stuck out for me was New Hampshire and Vermont. Though it's hard to tell for sure with a tiny unlabeled map. Anyone got a bigger one?
With Vermont, it's sort of notoriously infested with hippies. I'm kind of joking there, but there's a kernel of truth to it. Out of the three rural New England states, Vermont is always the farthest left, and in places there, Bernie Sanders would be considered too much of a centrist.
I'm not sure New Hampshire really falls into anyplace reasonable on the 1D Republican-Democrat axis, except for a standard deviation one way or the other from the middle, shifting with the winds. If you add in the authoritarian/libertarian axis to make it 2D, NH is pretty far up the liberty scale. No income tax, no sales tax, extremely minimal firearms regulation, hell, you don't even have to wear a seatbelt if you don't want to. The southern parts of the state are starting to turn into commuter satellites of Boston, to some extent, but it hasn't really eroded that "Live free or die" character.
Maine tilted pretty hard, with the rural 2nd District going convincingly for Trump. However, LePage also gets a lot of support and approval from those same regions, even now, with everything he's said and done, so we may just like blowhards.