Based on a combination of history, the traditional Chinese folk tale THE WATER MARGIN, and Jin Yong's wuxia stories, the leader of the Ming Cult during the time of Wong Seung's attack was an individual named Fong Lap.
According to THE WATER MARGIN, one of the individuals killed in the campaign against Fong Lap was none other than Gwok Jing's ancestor Gwok Sing.
It's ironic that Gwok Jing inherited the 9 Yum Jen Ging from Wong Seung, who had designed the 9 Yum Jen Ging to battle Fong Lap and his allies and associates. Then, in HSDS times, Chow Chi Yerk, an acolyte of the Ngor Mei Sect founded by Gwok Jing's daughter Gwok Seung, would use the 9 Yum Jen Ging to wreak havoc against members of the Ming Cult.
Seems like lots of bad karma between the Ming Cult and the Gwok Family, even though both parties opposed the Mongols.