Haha I just read that passage too and was about to list it as well. I'm hunting for any reference that Xiang Wentian made concerning Dugu 9 Jian. So far it looks like the only time was when he introduced himself and Linghu Chong to the Plum Manor guards. He claimed that LHC was Feng Qingyang's disciple but didn't specifically mention anything about DG9J. It could be that XWT simply made this deduction based on the fact that YBQ could not have produced such a talented student coupled with the fact that he knew of FQY's legacy.