I'm curious as to why they seem to think this would be unlikely. Religious zealots are one of the most significant modern right-wing groups. Christians fundamentalists are a dwindling group, so it's not surprising to see others fill in the gap. Plus, most of the anti-Muslim stuff was driven by propaganda to support the oil wars. Now, the "enemy" is Russia and/or China, so that's been retired.
Some of the alliances are more surprising to me than others. I'm not surprised that religious social conservatives eventually discovered that they have things in common with other religious social conservatives, even from other traditions. If your main issue is that you like the traditional patriarchal family and don't like homosexuality, it's not a huge stretch to find others who agree.
I'm more surprised by the movement in this direction of people like Tommy Robinson, former leader of the English Defence League (discussed in the article intro). I thought of this kind of far-right as more of a "clash of civilizations" type of cultural and/or racialist right-wing, defending "the West" against foreigners and immigration. They did not historically have much of a religious angle to them, nor particularly care about social conservatism (other than opposing immigration). It feels like a genuine change that people in that camp now find common cause with Islamism against a shared enemy of Western liberals.
