In my island game, there are 16 civ on a huge map with small islands. I have a huge army left after the war with japan which was on the same island. they are of course, extincted

so after I have build a lighthouse, it was time to explore. looking at the sea, a shallow part was near my capital, the border allow me clear view and i was certain an island was near my south.
with 3 trieme, i set out with 1 settler, 1 worker, 2 spearmen, 2 horsemen. there I found the indian.... they were technologically backward as they were alone. while i took alot of tech from japan before killing it. After i found a city just 6 block away from my capital, I decided to check the coast. it was comfirmed that only india was on the island, and there was no contact with anyone. being close to my capital, i wanted the island. I invaded, the whole india fell within 12 turns to my army of 30.
just as I finished the indian, a greek and roman landed 2 turns later and imediately builded cities in the broke cultural border.... they manage to build 2 greek & 3 roman city!!! ARGH!!! right in the land where the indian once was.... how did they know the land was emptied?
also, i took note that the AI seem to know which AI is more stronger, even before they got contact! (i know, as I can still sell them contact). The player advisor never once show which AI is better before contact. this is just plain cheat!
