Such are many of the names coined by creative minds using the early internet.
ETA: other meanings likely don't fit. It's not about self pontificating (well maybe only from Charlie's point of view), and the motorcar related to the Pope is already called the Popemobile.
It's thus sometimes unclear which people are "really" Antipopes until some time passes and you're like OK, Steve was an Antipope, the Roman Catholic Church still exists, the Pope is now this Dave guy, so his predecessor Geoff was also Pope, and Geoff's rival Steve's group died out, so Steve was an Antipope, even though for a few years my church said Steve was Pope, I now know that was wrong because God wouldn't let the One True Church vanish and once Steve died his whole church went back to Geoff.