Seeing two old-time EZA members get into a argument about Don's crazy talk is at once upsetting and hilarious. Let me add my two-cents...
I also watched the whole thing of Don talking about the pizza, has it been mentioned since (I can't keep up with all the content)? On my recollection, Don did seem to emphasize that the toppings were (or could be) on the pizza when this mysterious flipping took place, so I'm backing up @TokyoSlim on that. @Mbun, when you say "when professional chefs flip the pizza", what do you mean by "flipping"? I think the definition of flipping is part of the issue here. If you mean when they spin the dough in the air to form the crust circle, that's not flipping, and I believe Don indicated that's not what he was talking about either. I believe Don was indicating that he thought the pizza gets turned upside down during the cooking process, which, as @TokyoSlim said, is crazy talk.
Maybe trying to interpret what Don means about anything is a exercise in futility, and I doubt we'll ever get a better explanation from him, but when I saw that video, I had to post it.