US Chinese food vs Real Chinese food

I've hear people that were born in China and come to the US to try our Chinese restaurants say that they're very different compared to the food that's actually served in China. 

Can someone explain the differences in our perception of Chinese food and what's actually over there?

I used to frequent chinese places a lot, and I noticed that asians eating at the places ate mostly vegetables, and a shit ton of rice.  And the times i'd see the staff eating, a lot of times it'd be fish(nothing on the menu) and more shits tons of rice.