It's more.....personal? Professor Callaghan. He was the one Tadashi went back into the showcase to save from the fire. I didn't react to that so well, back home.

[Hiro wants to believe it wouldn't be a repeat, now. But even so. He wouldn't be thrilled at having the other around, even just knowing he was here. He understands in hindsight, more. But that still didn't excuse Callaghan's actions.]