He made sure to treat you at the business level, and

 

at the same time, tried to limit you to treating him at the personal level. Such disparity enhanced his dominance over you.

His insomnia was just a bait.

 

You cared. That should be a good thing. Imagine a place where nobody cares.

But everything comes with a price. Care also brings with it expectation, which burdens on people's unconscious because you have off-loaded it from your own shoulders.

He shoulders his own by not giving a damn. When he uttered "stupid design", it's like a dog barked for its master to hear, and the manager felt a great relief but still shouted "Stop it! Rover."

So, what you need to ask is: why do I care?  Is that they need my care, or I need to care? One has to be self-aware enough to answer.