Indeed its no more the cause of the accident then saying Max or Lewis waking up that morning caused the crash.
For me Horner's comment across to me was more to suggest that if the stop was faster, lewis would have filtered in behind Max avoiding them finding themselves fighting for the same piece of tarmac after the pit exit.
Of course i can also see the other side of this being a team principle is keen to place blame somewhere other then on his star driver.