Ffrom a 787 pilot on PPRUNE - the 787 compares the selected flap position to that required in the Flight Management Computer and will flag a warning if they aren’t as part of the takeoff checklist.
Regardless of where they started the takeoff role, they got airborne and were over 500ft up so that part isn't an issue.
I've only seen a short video so I say it's difficult to say what has gone wrong. Also, I'm not a 787 pilot.
But it is possible to take-off in ground effect and and then lose that lift once airborne but I honestly can't tell if that happened here. Regarding intersection take-offs - they're completely normal provided the correct performance calculations have been done.
However misidentifying the correct intersections has happened in the past and led to accidents - I know of one case where they overran the runway, taking out the runway lights before getting the aircraft airborne (with quite significant damage).
But as a modern aircraft - the 787 should have an on board warning system which will tell you if you are using the incorrect intersection (or if the runway length is insufficient - I've never used it though so I don't know the exact details of how it works). I think it may be an optional extra however - Boeings are like BMW's where you have to specify pretty much every feature you want when purchasing (for an additional cost, of course).
I suspect the FBW system on the 787 will not allow you so stall the aircraft (it will allow you to pull back to just below the stall and keep you there if you continue to pull back). If you're too slow you are still going down.
To me that's what it looks like. How it got so slow - I don't know, incorrect flap selection or some kind of mechanical fault, I would guess.
The 787 should be a very safe aircraft.
