saw another photo online that showed the dark black smoke cloud with taxing airplanes in the foreground. Obviously can’t tell from the photo if that would have been approach or departure end.

One other thing, I don’t see any rudder input, as one would expect ifthere was a single engine failure?

Surely the 78 has configuration warnings to prevent a flaps up takeoff? I generally don’t like to speculate, just trying to make sense of what we can see. Early flap retraction?