Looking at the photos and videos that are now available, it is possible to see why the reaction of the staff was so strong. The flames and smoke are severe:
https://www.theguardian.com/uk-news/...uttle-bus-fire
Stansted Airport bus fire: Flights resume after cancellations - BBC News
All of that aside, it should be no surprise that one pax said:
"Announcements were telling us to leave the building, but the doors were not open - so people began pushing and panicking."
another said
"It was the usual situation of very few staff on the ground and they were doing their best but they were saying they didn't work for the airlines."
Stephen Fottrell, a BBC journalist, was booked on Ryanair to Shannon. He told Radio 5 Live: “We were standing outside in the wind and rain for two hours.
“It was chaos, with very few ground staff.”
Passengers who were waiting for delayed services saw them simply vanish from the screens.