It's not quite as straightforward as that.
Contributory factor 5 was that "The manoeuvre took place above an area occupied by the public over which the organisers of the flying display had no control".
But that would have been the case even had the display been flown exactly as planned, rather than being a consequence of going off-track - there is no way that a fast jet display routine is going to stay within the airfield boundary at a location like Shoreham.