Sensei when written in Chinese charecters is pronounced as "Xian Sheng". Literally it means Mister in modern chinese. However in ancient chinese as reflected in cantonese (which is very much related to the chinese language spoken in Tang dynasty and at which time, Japan borrowed heavily from china culturally), "Xian Sheng" or "sensei" also means teacher. In cantonese, colloquially, we still call a teacher whose surname is Yang as "Yang Xian Sheng" or the Japanese "Yang Sensei" rather than "Yang Laoshi". In Mr Yang's case, Yang Sifu would be more preferable.
I don't know about Guangdong, but in Hong Kong, we address all teachers regardless of whether they are men or women as "Xian Sheng" or Sensei in Japanese. Mr Yang is from Shanghai. I don't know how shanghaiese in general address teachers. If shanghaiese like cantonese addresses teacher as "Xian Sheng", then addressing him as "Yang sensei" in the US is not awkward.
The author Wing Luk can be reached at: mailto:firstname.lastname@example.org