No, not all Chinese people are Buddhists, to give your question a precise answer. The dao and Confucian philosophy are also quite prevalent. In fact most of the Chinese people I know do not find that these three belief systems conflict with each other.
Nonetheless the majority of the Chinese people I've met in America are secular. Their involvement with the trappings of Buddhism, the dao and Confucianism are about as deep as Santa Claus or the Easter Bunny.
There is also a large minority who are Christian. In my experience many Chinese Christians carry on some daoist and Confucian traditions.
I've only met one Chinese Buddhist.