How is eating culture different in the USA and Japan?

Eating culture has big differences between USA and Japan. In Japan, we should finish our own dish; if you leave some food, it is rude in my country. However, if I finish my dish in America, the host will serve more food even if I’m full. When I went to Britain, I thought I had to finish my dish, and I kept going up to the limit of my stomach. I told my American friends that story, and she said Japanese eating custom is pretty strange, because Britain and America have the same eating cultures. I leaned eating custom from Britain and America, but still I feel bad when I throw away the last of my food. The biggest difference is that Japanese use chopsticks. I used chopsticks in America sometimes at the Japanese, Chinese, and Thai restaurants. I didn’t know some Americans could use chopsticks skillfully. One day my friend, who is coming to Japan soon, asked me if Japan had knives and forks, because he didn’t have confidence in using chopsticks. I almost died of laughing, and I thought he is native American.