They're just showing Charizard so they don't have to reveal what the new pseudo-legendary is.
Leak related things:
The now-credible-leak-that-predicted-everything-from-the-direct mentioned that some old Pokemon are getting dynamax-specific new forms. The reason he has a Charizard is probably because it was given one of those forms. I mean, Gamefreak wouldn't waste an opportunity to bring Charizard into the spotlight again, would they?
Despite what it got right I still want to doubt parts of it, like how Meowth apparently gets a Gigantimax form AND a regional "evolution"? After already getting an Alolan form? Come on Game Freak! ---