I spent a 32F and 37F night in the Ouachitas last week, in a hammock. My BA insulated air mattress failed the first night out, and all I had was an Oware 20" x 60" x 3/16" pad. I folded it in half and slipped it into the BA Mystic's sleeve, then improvised a Garlington insulator from my poncho and fallen leaves. I was surprisingly comfortable. So, if he had a decent pad or underquilt, he should have had no trouble in that regard. It sounds like he did think about what he was doing, and I'd assume he had appropriate gear.

I suspect something else happened that we just don't know about yet. Wonder if he fell in a stream or something? I can visualize him lying on top of the bag hoping to dry out some before getting into it... It's a shame.