A large percentage of the Hispanics in Texas are Catholic, and quite conservative.One thing I've noticed is that, at least in the wider Midwest, Catholics tend to be concentrated in the cities due to historical immigration patterns from Italy, Poland, etc. So if you take a look at Pittsburgh, Detroit, St. Louis, or Chicago, you'll see they have huge Catholic populations. But the surrounding rural regions tend to be mostly Protestant.
So because Catholics never had the same strong rural base, they were always much more prone to liberal influences. Of course there are exceptions like the Catholic Cajuns in Southern Louisiana who are religious and conservative, but still more laid-back about things like alcohol than the evangelicals to the north.
But like you mentioned have absolutely no problem enjoying alcohol.
A lot of Texas also has a substantial German and Czech ancestry which also tempers the teetotaler influence in much of the state.