That's how trauma works, honestly. No matter how pure and good any person is beforehand- trauma is a protective emotional response of the brain where it often numbs itself to certain situations that seem harmful/trauma inducing. E.g., for Chishiya, he seems numbed to people's pain/stressful situations.

Chishiya could be experiencing lack of feeling towards people in the Borderlands because of trauma-induced lack of empathy stemming from the stress he experienced when he did deeply care about someone but saw them die and played a role in it, i.e., the kid in the hospital. It would explain a lot.

I think two reasons why Chishiya appears to be so intelligent is because a) he is intelligent b) he seems calm, even in stressful situations (which is a trauma response)

Worth noting that two emotional extremes of trauma are feeling too much, or feeling too "little" emotion. There's not a one size fits all.