What I don't understand is why the guy in the cockpit jumped out, rather than trying to use the rudder pedals or tiller and steer the aircraft onto the grass.
Whilst aircrew (may) know where the brakes are I wouldn’t expect your average handling agent or ground crew to necessarily know where or how to operate.
If the residual hydraulic pressure or accumulator residual had fallen to an ineffective level then the aircraft would have rolled against the chocks with the slope at the first opportunity - making them very difficult to remove against the weight of the aircraft...?