Trump is happy with China because he thinks that China has made a big concession, and that he can tweet and take credit of of the largest deals signed in two days between two nations.
However, China is not giving free gift without any returns:-
Firstly these deals made US's East Asian allies looked bad as they did not give what Trump wanted during his visits, which is a political point scored by China.
Secondly, these are in reality, an exchange of goods for money which could be funded from liquidation of US treasury bills hold by China, which is in line with the long term trend of cutting down T-bill holding.
Thirdly, these goods and services are necessary for the needs of China which would be purchased anyway.
In short, these deals could be made with or with-out Trump, so instead of making many purchase deals over next few years, China merely put them all in place within two days to make Trump looks good, and made him a friend instead of an enemy.
