In this particular case (Post 464), catholic was referring to those who’ve grown up Catholic, just as methodist, baptist, and lutheran were referring to those who grew up Methodist, Baptist, and Lutheran, respectively.
Because all were not capitalized, I would not see it as pejorative to any one group. It might not be proper grammar but I don't see it as insulting. If only one were consistently not capitalized, then you'd have grounds for complaint, IMO.