From 2013: "If I end up being able to make this game at some point, we all might find that it fits nicely in between Monkey Island 2 and Curse of Monkey Island." https://grumpygamer.com/just_to_clarify_point_12
The game announcement states that it "picks up where Monkey Island 2: LeChuck's Revenge left off". These two facts do not have to be mutually exclusive.
I thought the implication from this trailer was that Ron Gilbert agreed to do this game if he could ignore the story and characters from the other games (which is why Murray is getting pushed off the deck)
It's amazing how many interpretations of this joke people appear to have :)
To me it's very clearly about Gilbert's past remarks that he'll never do another Monkey Island unless he fully owns the IP. Tossing Murray into the water means "yes, I don't own the IP and yet I'm making another Monkey Island, you can stop pointing it out".