[The Panther]

On turn 22 on any size map, a decent player can have scouts all around you, waching your every move. The first indy with scouts to recruit means continuous scout building for many turns. All you have to see is one red candle during exploration and they know you are there.

I think the computer might have total vision, though, but I promise you that this can happen in MP. Expect it, especially in a 1 on 1.

As for declaring war, when you are the only opponent of a single AI, you should expect a war declaration, and maybe even earlier than turn 22. With a third AI opponent, like you had, this is not as certain.