Why? The descent of the Peyresourde is one of the easiest out there, bar some hairpins at the top and a couple halfway down, it's virtually straight all the way down.
I'd say he caught them napping and had a go for the hell of it.
You are probably right. It was just very different to what we are used to from Sky or Froome. It was also unusual to see him push the pace a couple of times on the climb without distancing almost everyone else. I'm probably reading too much into it.
I make Quintana favourite after that. A top form Froome doesn't bother with stunts like that in my mind.