Yes, it seems that way to me. I also agree with what Vainamoinen smartly wrote about the secret and the meaning.
It is a very good question, since we can speculate, make assumptions and still not have the answer. This is one of the nicest things in MI2: it creates a world that can be interpreted by the player in a number of ways and on a variety of levels, without one way or level contradicting necessarily the others.
So, if it is all a fantasy, we could also think this: Guybrush imagines that LeChuck doesn’t want him to find Big Whoop, so that the game doesn’t end, while Chuckie on the contrary has to find Guybrush, put an end to the game and take his brother back to their parents. But this is just one of a thousand hypothesis. We could also assume that nothing that happens after the rope breaks and Guybrush falls down into the dark is strictly real (maybe Guybrush dies after his fall and that’s why the original idea for MI3 was ‘Guybrush chases the demon pirate LeChuck to hell and Stan is there’? Who knows). I’d like to point out that if we take the Star-Wars-parodying ending for real, then we must suppose not only that Guybrush and LeChuck/Chuckie are brothers, but also that the entire world of Monkey Island is a masquerade, a play in which the actor who was given the role of LeChuck wears a costume not very different from the Mardi Gras costume worn by the woman that guards Elaine’s mansion on Booty Island.