This doesn't seem terribly surprising given the church's position on hot-button issues like abortion. But it's also worth noting that registering as a republican doesn't mean you've voted for every republican on the ticket (and vice versa).
Illinois doesn't have party registration and the entrt reflects voting in a Republican primary. That might indicate a Republican preference, or it might indicate perceiving the potential stakes in the Republican primary contest as higher, because, e.g., having a much stronger preference that a particular Republican not win than any preference among Democratic candidates.
