Since it says that he was a teacher, could they be using it to say that he was not an official ordained priest?
https://en.wikipedia.org/wiki/Laity
https://en.wikipedia.org/wiki/Priesthood_in_the_Catholic_Chu...
To be clear, I'm not OP, and I don't judge the quality of the article on this basis. It's commonplace to see a journalist do sloppy work, especially in parts of an article less critical to its thesis. But the article already defines the term 'catechist', albeit incorrectly. I don't think it's unreasonable to consider that the same trouble should go toward getting it right.
The silly objection here is like objecting to the statement "he was a pilot, an airplane driver", because a "driver" drives a car, not a plane.
As I said, I think OP makes too much of the phrase, but I agree it's entirely risible.