You are correct, most of it is tumbling and stuff you see in Chinese Operas, but alot are Wing Chun. Surprisingly, Jackie Chan also takes Wing Chun. His speed with the wooden dummy (also shown in Rumble in the Bronx) is quite good and I recognize most of his punches to be WC style.
Oh and btw, me and Sammo are distant cousins.
His background as is Chan's, is in Peiking Opera. He, Angela Mao and Jackie also learned some Hapkido in Korea.(can't at this moment recall the teacher's name..he is rather famous) Sammo is also a big wing chun fan. As far as his knowledge of it, I'm not sure it's real or his interpretation.