If I ever get a chance to write a paper on this aspect of the comic strip for one of my graduate symposiums I will be sure to send you a copy, because I am fairly certain that if I sat down with the entire run (or even a sizable arc), I could come up with lots of things that indicate just that. . .
Personally, I think to say that "PC" and "NPC" just happen to mean something different here when every other game term is used basically correctly (even if the exact rules aren't always followed - heck, most tables have some house-rules or hand-waving

) is just a matter of convenience to avoid the double narrative suggested by any role-playing game. Heck, there may even be a triple narrative because the characters seem to also be aware of the fact that they are "in a comic strip".