Chinese =/= Han!
This so-called historian can't even get this basic fact right and keeps using the wrong term.
For the sake of the discussion here, the most authoritative viewpoint is that of the Song. The fact that modern China's interpretation considers Liao Chinese doesn't disprove the author's statements. You need to back up your statement with proof that the Song considered the Liao (and the Xi Xia) Chinese. I've posted numerous quotations of Song officials wherein they refer to the Liao as barbarians or a foreign nation. If you cannot provide evidence, then we will have to conclude that you are suffering from