If I am a nonresident alien (China). Do I have to pay income taxes on my income from the US? (Unearned income). I have been in the US for less than 183 days in the year.

Ask questions on the sprintax site:

NON RESIDENT ALIEN  

If you are a non-resident alien, your return must be filed on Form 1040NR, which cannot be prepared using TurboTax.  You can use TT’s partner, sprintax:

https://www.sprintax.com/non-resident-alien-tax-1040nr-turbotax.html

But I understand that China has a Tax treaty with the US that prevents double taxation.

This is why I am a bit confused.

https://www.irs.gov/pub/irs-pdf/p901.pdf