Don’t think it was much to do with trim as they were able to achieve a body angle greater than that for a normal rotation without leaving the ground, initially. That shows they were too slow for the aircraft configuration.
Whether they used a different flap setting than planned and/or the wrong speeds (weights) I don’t think you can tell. It does look like a fairly gross error, though.
A V1/Vr mixup is possible as technically you can have a V1 split off a 4,000m runway if you want but it's most unlikely IMHO.