In my episode review of this episode I interpreted that scene as him actually being pretty observant of people in his immediate squere. Since he comments on Zhang Ruonan's coursework she seems to be in his department (so his sphere).

I think, especially with that student he insists on being innocent, that he tends to assume the best of people (despite having ample evidence to the contrary via his real job.)

Whereas I believe Yunlan is a person who'd be a bit of a cynic regarding humanity (excepting his team though obviously).

But I totally agree that he'd be even better in long lasting relationships. Li Quian definitely counts there.