Yo, English is not my first language either so if I am mistaken pls someone correct me.
Past perfect is used when you are talking about thing that lasted (not only happened) in the past and ended in the past. Just like dont uwu me wrote narrator was referring to the very specific event in the past that took place and now it no longer last. Example:
"The smile of relief on Cameron's face seems to break the dam of emotion in Dev's chest. That wild look he had earlier...
this is past simple and the wild look in this one is just a short glare, however Cam was making this face for a long time. There is more to Past Perfect but i am not enough informed to answer. Next one:
... the one that had looked at him as if he were a stranger is gone. "
in this one had is important because if you removed this word you would get this sentence: the one that looked at him as if he were a stranger is gone. Now we got a sentence where someone someone is looking at Cam and we know it is not a point.
I hope it is helpful and I haven't made fool of myself :)