Pic follows a middle-aged woman who sets out to take revenge on her unfaithful husband.
Lou has been banned in China for his films, which often deal with political themes unpopular with the government.
“Mystery” also took home the award for best newcomer, Qi Xi, and best screenwriters.
Kitano Takeshi from Japan nabbed director honors for “Outrage Beyond” but did not attend.
The Philippines dominated the acting section, with best actress going to Nora Aunor for “Thy Womb,” and 87-year-old Eddie Garcia picking up actor laurels for “Bwakaw.”
The awards, inaugurated in 2007, recognize achievements of pics from across the region.