The battery was not being charged, from a train socket or otherwise - it was being carried in a rucksack.* When the rucksack started smoking people panicked, thinking it was a bomb - not unreasonable given that bombs in rucksacks were the chosen method of the attackers and would-be attackers in London in July 2005 and elsewere in the world more recently.
This caused a panic, and people trying to get as far from a possible explosion as they could - again, not an unreasonable reaction. The platforms at Dalston Kingsland are narrow and would be crowded at that time of day, and there is a lot of railway land south the south and west where the line to Dalston Junction diverges from the North London Line formation, so people moving on to the track is very understandable in the situation.
Had a member of staff been standing next to the bag, and immediately recognised that it was not a bomb there is a very small chance that they may have been able to prevent the panic, but
(a) there is a small chance that they would be standing next to this particular passenger, particularly if they were not adjacent to a door (I don't know).
(b) if they were anywhere else on the train they would not have been able to do anything - the trains are so crowded in the peaks that moving through them is essentially not possible.
(c) There is no guarantee that even if they had been in the right place, they would have instantly known that it was not a bomb. I know railway staff do get training in identifying suspicious packages, but they are not experts (and even the who are don't always get it right, even when they have time to make a considered decision) and will presumably treat something as suspicious if they aren't certain.
I am very much in favour of trained staff on board trains, but this is not an example of an incident in which they would likely have made significant difference. There are plenty of examples of incidents in which they would though, so it's really not worth fighting the battle over a bad example when there is no shortage of good ones.
Another member of staff might have helped in the immediate aftermath of the panic, but it would make essentially no difference whether they were train or station based. Indeed a station staff may have been more useful as they would be more intimately familiar with
the station and its immediate environs.
*My completely uniformed speculation about the cause is that something else being carried in the bag shorted across the battery terminals.
