Bagged blood. There's really nothing else that does that overnight and was the whole deal with Aderlass.What strikes me is this ability to rebound after being on the down side in the last couple of mountain stages.
He looked to be fading in last year's Vuelta as well (losing a minute to Roglic, Valverde and others on Becerril de la Sierra) only to completely erase the field a couple of days later and get his spot on the podium.
Now exactly the same happens in the Tour. There must be something to it.