When Xiao Feng realised that his father was still alive and was actually the one who commited all the crimes, his reaction was to take the blame of his father's crimes onto himself. That was probably the filial way to do things back in those times.
However, the question is that amongst his father's crimes were the murder of the Qiao couple and Reverend Xuan Ku. If his father had just killed the others like Grandpa Tan and company, its easy enough to accept. But the Qiao couple brought him up and Xuan Ku was his teacher. In the wulin world, the teacher is supposed to be as important as ones parents. You also can't use the defence that they were responsible for XYS's plight since neither the Qiao couple or Xuan Ku were party to the ambush of Xiao Feng's parents. Of all those victims, the Qiao couple weren't even part of wulin. They were just peasants.
If Xiao Feng had repudiated his ties with XYS based on the murder of hs foster parents and teacher, would that be considered un-fillial? Not saying that he should repudiate his Khitan blood, just his father.
What do you guys think? Do you support his decision at Shaolin?