Although never stated outright, it is strongly implied in LOCH that Yeung Teet Sum was descended not only from General Yeung Tsoi Hing of the Southern Sung Dynasty, but also the famous Yeung Family Corps of the Northern Sung Dynasty, who had fought against the Khitan and Hsi Hsia states a century or so before LOCH.
According to one version of the Yeung Family Corps legend, Yeung 4 Long was wounded in combat against the Khitan, taken as a prisoner of war by the Khitan, nursed back to health by a Khitan princess with whom he predictably became smitten, and ultimately defected to the Khitan side, thus becoming a traitor to his country and his family.
Maybe Yeung Hong in LOCH was following the precedent established by his ancestor. The Yeung Family Corps mostly produced valiant heroes, but once in a while, it produced a traitor.
Notably, both characters were portrayed by actor Miu Kiu Wai for TVB during the 1980s.