Have you ever completely misjudge a friend or relative's politics?
I have an uncle living in Nashville. He's a doctor, mainline Protestant and bashes Obama and Tea Partiers alike. Solid Romney man right? Wrong. He mentioned that he voted for Rick Santorum in the GOP primary a while ago and I was completely taken aback 
Well, if he's a socially conservative (since he does live in Tennessee
) Protestant, even if he's a mainliner, Romney's waffling on social issues and potentially, his Mormonism could have been issues for him (Just speculating here
).
Also, isn't your family from a strict orthodox Calvinist tradition? And isn't that tradition both very conservative on social (and I guess political) issues, as well as being more "High Church" than many other conservative Protestants in North America (aka politically conservative Low Church Protestants who aren't affiliated with a mainline denomination-aka "white evangelicals")?
Therefore, if your uncle is indeed more "High Church" and "traditionalist" in his conservatism (I'm assuming he's similar to you in that regard, correct me if I'm wrong!
) maybe supporting a politician who is known for both his devout Catholicism and his outspoken social conservatism isn't so surprising.
