Hmm. Obviously, what I'm about to say is from the outside and based on the 'facts' in the newspapers. I am heavily involved with cadet forces adventurous training, so do know the rules and procedures that should be followed.
My first thought after seeing they were now OK was the dreaded 'ratios'. This is 1:6 (or 1:8 if the members hold summer mountain proficiency or equivalent). The papers quote between 7 and 10 adults to 63 cadets. That would appear to put them outside the ratios, even if all adults were qualified (ML etc.) I am also puzzled that they appear to have been together, rather than moving as separate groups (perhaps they came together due to the issues).
My second thought was to do with the predictability of the weather, and I do not know what the forecasts were. Nor do I know how well equipped they were.
On seeing more details, I can see a possible timeline. I am guessing that the ankle injuries caused them to be unexpectedly stopped and exposed. Staff made the precautionary call to abort the trek and request help getting them to safety. That sounds like a sensible thing.
Probably the most significant quote:
"the group leaders had done a good job in protecting the teenagers." - medical director of the NI Ambulance Service
So, it seems possible that they were technically operating outside of the rules but made a good call on the ground.