I'm not sure of it as well, but it was the first thing that some of the analists on the Belgian tv were thinking of.When there is someone or something to criticize they don't refrain from it tbh.
Like King_Eric said, mechanical problems is not accident so there is no moral obligation to wait for the opponent.Plus apparently (I'm not sure of it) it was Andy's fault so why should Contador have waited for him ?
But it shouldn't matter anyway. There's no racing sport in the world I can think of where people wait for their close competitors when they have mechanical problems.