Correlation is not causation. Hispanic, Asian and Black voters of non-Catholic religion strongly indicate against causation.
If we are to make an argument for causation from correlation, then logic requires a comparison and look at the strongest correlations.
Based solely on correlation, a causation is much more likely to be the result of the higher number of non-white Catholics vs the more white makeup of non Catholics in the sample. We see this most obviously in the difference between white and non-white Catholic votes.
Correlation is much stronger for other factors than Catholic/Protestant. Let’s just take white/non white. (Remember that white includes a large range of possibly relevant ethnicity as well):
Here’s Fox’s Exit Poll results..
Vote by Christian, whites and non-whites
Obama Romney
White Protestant/Other Christian 30% 69%
White Catholic 40% 59%
Non-white all 80% 18%
The best predictor of vote here is non-white vs. white.
The best predictor of vote regarding Christian religion in total is church frequency:
Obama Romney
More than once a week 36% 63%
Never 62% 34%
The best predictor of vote regardless of religion is race/ethnicity.
Obama Romney
White 39% 59%
Black 93% 6%
Hispanic/Latino 71% 27%
Asian 73% 26%
Other 58% 38%
Hispanics are recent, the catholic vote is never changing.
Besides, it is a single denomination, a single church, all members of the same denomination.