For those of you who are looking for some context, and have an hour to spare, Ahoy made a great documentary on YouTube about ‘The Secret of Monkey Island’ that touches on this topic. [0]
The source material linked in this thread looks to be more authoritative than the video, and if I remember correctly the video even gets this detail of the story wrong, but sometimes it’s nice to know the story around the story.
The closest we ever got was in a recent stream with Ron Gilbert himself (from https://gamehistory.org/monkeyisland/). Jump to 4:29:23. If only there wasn't a cutscene :-)
The interviewer was making a joke by abruptly cutting to alternate versions of the Monkey Island 2 "interrupting" cut scenes and Ron was playing along with the joke by implying that their conversation continued during the interrupting cutscene by coming back out of the cutscene's with garbled mid-conversation, one of which was essentially "...and now you know the secret" as if it was given away during the cutscene. (It likely was not, as again, Ron and the interviewer eventually made it clear the gag was a gag. Even if it were, it didn't make it to the stream.)
The stream is Ron Gilbert being interviewed about various fun trivia for Monkey Island and its development. While they do that, they show four cutscenes (one per map piece for MI2) that didn't end up in the final product due to size limitations. Also during the stream he describes that those scenes originally popped up randomly during game play but they change it to only happen when you exit a room.
So they randomly played those cutscenes during the stream and the one I linked ends and the stream switches back to the interview with the interviewer saying: "... so that's pretty interesting that this would be the secret" :-)
Actually I think the secret is probably a total let down. The MI games are (potty) humour kids games (which nobody in my country due to lack of language skills realized, and it felt much more mature and cooler than it was intended)
Well it is all theme park style (not too surprising since it was inspired by the pirates of the caribbean ride). MI1 : map seller, MI2: parents picking up the kids, alleyway like the alleys in MI1
The source material linked in this thread looks to be more authoritative than the video, and if I remember correctly the video even gets this detail of the story wrong, but sometimes it’s nice to know the story around the story.
[0] https://youtu.be/9F9ahZQ7oP0