Yang Qing carefully sorted all he had read about the Blue Soul Flame Crow Syndicate and correlated it to the information he had gathered over the past few days.
After he heard from the Imperial Secretary that the King's grandfather had suffered some sort of relapse just as he was about to deal with his final injury, Yang Qing instantly assumed foul play considering his existing suspicions about the kingdom.
Part of his theory operated under the fact that there had to be someone from the Deer Mountain Kingdom working with the Blue Soul Flame Crow Syndicate to ambush the obsidian serpents' daughter.
However, that theory had a few holes in it such as what the collaborator from the Deer Mountain Kingdom stood to gain and the exacerbated injuries to the King's grandfather answered that question.