Some people are serious religious fanatics. They will kill to further their beliefs. Other people are crazy. They will kill just because they are crazy.
This guy seems to be in the second group.
The 2A is the best protection against either group. And so many churches have armed parishioners known to the pastor on security duty. But I’m sure the Catholic Church does not. That’s their right, of course.
Some Catholic parishes do, others don't. Whether it is allowed depends on the particular bishop's policies in that diocese.
It is a distinct possibility however that many parishioners carry without the priests knowledge. The more traditional a chapel is, the more likely someone is carrying.