“Parishioner” refers to those attending a Catholic church that is organized by geographical parishes. It does not apply to any member/attendee of a Protestant church and most definitely not a Southern Baptist Church. It’s a usage that wouldn’t have slipped by any editor worthy of the name and job. That function does not exist in modern online “journalism”.
Oh, Merriam-Webster has it somewhat different, a parishioner is “a member or inhabitant of a parish” and a parish is specifically for “a local church community composed of the members or constituents of a Protestant church”
I don’t doubt yours is probably a much more original definition, and theirs is simply reflecting more Left Wing influence.