Thor actually rode Rast(?) into the barriers after being forced that way by a FdJ rider.
I just watched the slow motion overhead replay about 5-6 times and it was one of those that was hard to really blame any one rider definitively. A FdJ rider led out the sprint and Gilbert came around him on the left, which pushed the group towards the barriers on the left. Another FdJ rider was on Gilbert's wheel and he followed Gilbert left which pushed Hushovd left, which pushed him into a fast moving Rast, pushing him right into the barriers. Hushovd went back into the FdJ rider, who fell into Hushovd, pushing him back into the barriers.
It was ugly. It was always going to happen once Gilbert started moving left. I guess you could say he caused it, but I don't know if you could say he was at fault. He had almost a bike advantage when he started passing the FdJ rider to the left and it was a very gradual move.