
Dan was just told not to drink on his medication, the fact that he's continuing would be frustrating for anyone who cares about him. Watching your loved one destroy their life and health is devastating and exhausting-- it's not KD's fault but change needs to happen. And while I think JK doesn't have the awareness to realize WHY KD's choices frustrate him so deeply(aka, just writing this behavior off as annoying or pathetic to avoid actual reflection on why he cares so much), it reached a boiling point. His reaction is far from perfect, but it's a clear and stern response.This is a wake up call for both characters and hopefully a turning point in character development for JK.
I think what OP meant is that since the doctor basically told them that KD might die if he keeps on drinking, him not stopping is like him saying "I don't care if I live or die" and that's what's triggering a strong reaction in JK (= proof that he cares a lot about KD) but since he's bad at emotions, he doesn't know how to express his anguish and worry in another way than getting angry/agressive. The last panels are him properly showing worry/relief = you hug the person you care about/tell them you care about them, you don't blame them/yell at them. But he's fucked up so it'll take time
Thank god for the officials. Thank you uploader!