I suspect that the monotone "Brace Brace" and evident complete lack of any passenger control on the part of the FAs didn't do much to help matters.
The crew were chanting this as passengers started to clap - I started to chuckle while watching it. It completely failed to convey any kind of importance, yet alone urgency or danger, in its delivery.
Who knows what information the pilots were privy to; but it seemed there was very little time in-between the remaining engine being shutdown after the aircraft came to a stop, and the order to evacuate being given. In my mind's eye, I could see the Emergency Evacuation checklist being actioned; after the engine was shutdown, there were the three dings, then the command to evacuate. I could not see evidence of smoke or reduced visibility in the cabin at any point in the video (sure there was haze/smoke in the other video) that showed the start of the evacuation.
Why the unseemly haste?? The only suspicion that comes to mind is that poor information was conveyed to the pilots.
I'd be very embarrassed if I were in the safety/emergency procedures training department of JetBlue. Something very unsatisfactory transpired on this occasion.
But, hell, no one was hurt this time, so it can hopefully be used to fast-track changes in procedure to plug glaring holes in their system before somebody does get hurt.