Steve ,
But ... but ... that is what marks joke was all about!
Although I assumed the people here know that, I also assumed they have been using it as a given, and that they do not quite realize the "why" of it anymore (would take a few moments to realize it). Asking them to come up with an explanation why marks statement is false is just making (a bit of) fun about that.
... which still nobody has done by the way. Yes, your above is certainly the point of it (and has been mentioned before). But as an explanation which others (the novices under us) can follow and (be able to) agree too it doesn't quite do.
Oh well, maybe I just stretched it too far.
Regards, Rudy Wieser