[Tadashi nods along as Hiro repeats his own words back to him. That conversation seems a long way off now, with so much strangeness between then and now.]

He was afraid.

[He knows Hiro must've seen it. He might not have registered it in that moment, but in the time after? The hours in the hospital, the days spent in bed afterward? There'd been plenty of time to process what happened that night. To go over things from every angle, to find what went wrong and where. Tadashi could see it, and if he could see it, he knew Hiro could too.]

That doesn't justify attacking Baymax like he did, but that signal did something that we didn't intend, and he was confused and afraid.