As I read article 19 , for you to be able to assert treaty conditions of the said article you must establish (1) you are or were a resident of the other contracting state ( china ) ; (2) you are TEMPORARILY present in the first mentioned state ( US); (3) you are in the first mentioned state (US) for the primary purposes of teaching, giving lectures or conducting research..
The trouble here is that you have adjusted your status to "permanent resident" and thus requirement (2) mentioned above is not satisfied. Thus I feel you are not eligible to assert treaty benefit request.
The whole article is reproduced below ( from which I picked specific parts for my stance):-->
ARTICLE 19
(Teachers, Professors and Researchers)
An individual who is, or immediately before visiting a Contracting State was, a resident of the other Contracting State and is temporarily present in the first-mentioned Contracting State for the primary purpose of teaching, giving lectures or conducting research at a university, college, school or other accredited educational institution or scientific research institution in the first mentioned Contracting State shall be exempt from tax in the first mentioned Contracting State for a period not exceeding three years in the aggregate in respect of remuneration for such teaching, lectures or research.