and the cap was the bloke who opened an exit by himself.
I would like to know how JetBlue briefs passengers seated at emergency exits...
For a lot of airlines these days there is no briefing at all, and the pictographic instructions just tell you, not to open the exit in case you can spot a fire outside.
So matter of fact that bloke may just have done what he was poorly instructed to do...
Must problably blowed out as a result of explosion.
Alternatively indicating that someone forgot to lock the thrust reverser correctly... It happened before for fan cowl doors, it may happen for thrust reversers as well, but with a totally different effect. After all the airflow which produces the fan thrust blows through it, and the engine will probably not like a half blocked passage at climb thrust...
But the report will clearly indicate the root course of the engine trouble, so no need for speculation.