Assuming the aircraft was a PA28-151, take off distance over a 50ft obstacle is 540M.
There is 630M of runway between the intersection and the far threshold - the backtrack doesn't make any sense to me at all?
If it wasn't a PA28-151, and some kind of 'hotter than a Pitts' hot ship, then the backtrack makes even less sense!
glush mentions in another thread that he instructs on a Eurostar - so perhaps that was the aircraft in use on the day?