Don't manipulate your shidi
The trials of the Dragon are a clever ruse for Heavenly Dragon sect to have a legitimate way to get rid of disciples it deems 'undesirable'.
The trials consist of a series of challenges of ever increasing difficulty, where the disciple is supposed to either surpass them or die trying -- their death being regarded as proof of their guilt.
What they are guilty of exactly is left up to the sect masters' whims.
In Xi Zirui's case, he's being accused of collaborating with a known spirit creature, responsible for the destruction of a human village, and the death of several humans.
No one brought up any suspicions of him being a spirit animal himself, but that doesn't mean no one is thinking about it.
Han Chang doesn't strike him as someone who needs a valid suspicion to frame someone.
Su Xueyi frets like a mother hen as soon as he learns of the news.