He must have been on the rivet and if he'd followed Trofimov risked getting hit by Landa then Aru and losing out anyway. As far as I can tell. He still stole a few more seconds I suppose.
Contador said something to Aru a few seconds after Trofimov attacked. In my mind it was: "He can go, you can't." I don't understand why Contador wouldn't have followed Landa otherwise - it didn't even look like he thought about it (unless we was toast, but he did make a little dig near the end).
He must have been on the rivet and if he'd followed Trofimov risked getting hit by Landa then Aru and losing out anyway. As far as I can tell. He still stole a few more seconds I suppose.