The difference is those Europeans sent people to China, and it took many years. Once there, these Marco Polos didn't demand China give "x", and if refused, declare war. And the Chinese, victims of these impetuous (and historically nonexistent) declarations, didn't suffer the downsides of being at war with some platform shoe-shod jerks half a world away who couldn't possibly be a threat.

The game mechanism is fubar. It takes rumors of a civ's existence to be a basis for direct communications. They didn't have telegraph in 2000BC, you had to go there.
I prefer my cheese on pizza...
Thanks, but I know how to do it (I stupidly gave communications trading to one of the AA advances in the mod

), I just wondered if it did more than the obvious in the game. The way this game is programed, it's not unusual to change something and have other things changed that were unexpected.