Some comments mention the overwing exits in the wrong context.
FYI, LR3 on B773 are manned by cabincrew. It's not like the overwing exits in 737, where you brief pax how to open in case of emergency.
They are normal sized doors fitted with escape slides. The only difference is that pax would get on the wing, turn aft, make few steps and jump and slide. The slide is belly-fairing mounted, not part of the door.
Pax should always follow crew instructions. My believe is that cabin crew were standing by to evacuate if the conditions got worse inside. As we can see in the video there was no
smoke inside. It was one of those 50/50 situations. Everyone was ready to evacuate but they waited to see if the RFFT puts the fire off fast enough not to initate an evacuation.
Also, cabincrew are very well trained on how to assess the situation in and out. The assumption that they could have opened the doors that had hazards outside it's a bit unrealistic. You need to know what training they get before you judge them.