To be honest you can't really blame the passengers in this incident (or the last one) for getting off the train, I wouldn't have done but I can understand why they did. From the photo posted earlier the train was barely 60 yards outside the station.
There's no Alpha male about it, false bravado, "want want want" etc, simply a desire to escape a 35+degree oven having been given little or no information of when help will be at hand.
If there's a genuine emergency talk to the train crew or dial 999 but there will be little sympathy when it turns out it's just a temper tantrum with no mummy around to make it better.
Which is, I'm afraid, an extremely poor, unacceptable attitude to display towards a paying passenger in your care who may be frightened, suffering any number of complications, claustrophobia, diabetes etc the list goes on.
The fault is with the way the industry is these days and lies with the TOC's and Network Rail for not having adequate provision to deal with incidents like this. Procedurally the situation should have been managed such that the passengers were kept informed at all times and controlled so that they wouldn't have felt they needed to escape. In my opinion it is simply unacceptable for passengers to be abandoned on a stranded train for that length of time in that amount of heat with so little information.
As stated - I would not decamp from the train without authority - but I can well understand why people did. There needs to be a top down review of how TOC's and NR deal with situations like this, and on the BTP side how they respond to genuine cases of wilful negligence, damage & trespass.
Until that takes place and the various links in the chain are properly joined up from traincrew to NR engineer fixing the fault, this will keep happening, and the passengers can't be blamed for it.