/u/Shlin28 answers a similar question a couple of years ago. https://www.reddit.com/r/AskHistorians/comments/49oaly/what_did_the_romans_know_about_the_chinese/d0ti5j0/
Again in this question he/she links to previous question but answers extra questions
In the threads it's said that Rome did know of China via silk road stories and via Greek and Persian traders.