It may well have been an engine failure, but surely their limited Mtow should have factored this in. If an engine stops above V1 you'd be expected to continue the takeoff and have the required performance to get airborne before you run out of runway. They clearly didn't achieve that, so if it was just an engine failure I think you can still safely conclude they were indeed too heavy!
Or its an engine failure and the remaining donks weren´t up to it...