If anyone else had said those words just now, it would have sounded like they were suggesting Guan Han's death was suspicious and that Su Ren was deliberately trying to tarnish the Emperor's reputation. But coming from the Emperor himself, it came across as harsh and confrontational.
It sounded like the Emperor was trying to clear himself of suspicion by deliberately coming up with such a story.
Of course, Qi Junmu could also forcefully suppress the matter, but doing so would cause great harm and definitely leave hidden dangers. It could become something others would use against him later.