Are there anymore easter eggs other than the treasure chest?

Not that I have heard of.

What is an Easter Egg?

The short answer is that they are hard-to-find hidden things in computer programs. Wikipedia has an in-depth article on them here, if you want the long answer!

How do I find them?
Can I find them in Virtual Villagers?

The only way to find true easter eggs in a game is to go "hunting for them" by trying different things (or by having someone tell you where they are and how to find them). There are really no true easter eggs in Virtual Villagers. There is a "hidden object" in the game, but it's also one of the puzzles and is an obvious part of the game, which is not a characteristic of actual easter eggs.

I wonder what the message: "Sees something unusual" is when a master walks towards the treasure chest....
(and not just "Admiring the treasure"

I have always wondered that too. I have had that happen several times. One of my villagers is heading near the already disconvered treasure chest and looking towards the ocean when they will say they see something strange.

It's just a minor bug. That's supposed to be a clue to the location of the puzzle, and should not appear after the puzzle is completed.