Though Prost still would have won if he hadn't clipped that barrier like quite a lot of other drivers (did it move or something?)
Senna said one of the walls had moved to cause his impact with it. Pat Symonds said he went to check and was astounded to find that Senna was right. Not sure of how exactly he knew that the movement had come from an earlier impact rather than Senna's, but that's a moot point - the blocks could indeed move.