Well, if it's like what you're saying then the description is incomplete.What makes you think it isn't both? They're actually the same thing:
Essentially, whenever a character takes a title that has an appropriate male_names or female_names tag, they will get randomly assigned a regnal name. That works whether they get elected Pope or are randomly created to fill a title.
Clearly this could cause weirdness if a character takes a 2nd such title, as they'll likely get a new regnal name based on the new title.![]()