I'm not commenting on the actual incident (I'd rather not speculate) but more in response to the posts regarding the use of driving controls above...
While my driving experience only goes as far as the very-occasional 25 mph trundle in ex-BR locos with D&M / Westinghouse brake valves and the few-times-a-week 5 mph shuffle around the depot in modern PBC fitted units and also the odd shunt loco, but I find it difficult to understand how you can be sat at a driving desk of a train and be so unfamiliar with it that it can result in having little or no control of the task being performed as suggested above. The motion of applying the brakes, with a power-brake controller is the same or at least very similar to using a separate brake controller / valve - ie. forwards for progressive application and eventually into emergency. There are also separate emergency brake plunger-type devices should there be an issue with the PBC. When sat in a PBC fitted train, theres not much there that normally involves controlling the 'stop and go', it's the PBC and it's not even something you have to go looking for either!
In the highly unlikely event that the PBC seizes and all the E-stop devices fall to bits in your hand, open a door and break the interlock - or - if you're completely desperate there's usually a backwall of (brake control) MCBs you can trip, but that's not something I expect will ever be required to know in training. Of course theres the DSD too, but that's never a fun thing to wait for, longest six seconds or so ever.