Hickey shrugs in a sort of 'mate, I don't know either' kind of gesture. Because he really doesn't know why that was the breaking point. He's not the sort of person who cares much about things like 'souls' to begin with. They might exist? But they also might not. And anyway, it's not like it matters after you're ripped apart.

"S'pose it was his breaking point," he muses. "Man can only take so much stress, after all. And everything related to the expedition was very stressful."

Even if you didn't take into account the murderous bear god, it was still a rough time.