But it may have been also because the lateral cg limit would be exceeded and the ailerons couldn't counteract the roll
Probably the case yes.
I used to flying for a drop zone in the early 90's.
One day a regular jumper came up with the bright idea to wing walk a C-182 before actually jumping from it.
"Just for fun!"
"Sure! why not"
Dumb and happy we were I think!
We did a good brief though! Location, direction, duration of the jump run and how he would manage that.
I can't remember for the life of me how high we were exactly. Just not low for sure, probably around 8 or 9000' which was our standard jump's height at that time.
So a good margin for screw up but less for our C-182's performances.... Euphemism!
He practiced a few times on the ground and said that with the wind blast holding him on the leading edge, it would be much easier anyway.
Ok, sure...
Off we went.
A first group of 3 took the exit, he went right after them on top of the wings.
I could feel his weight moving around very easily. 150lbs top with his parachute's gear!
Then he decided to go in the center box, which wasn't briefed! That sh!t move works well on a twin tail like a B-18 but not on a Cessna.
It totally altered the airflow on the tail, to the point that I was getting worried to loose controls.
He must have felt my hand banging on the ceiling pretty hard, or the 182 going very mushy under him. Either way he started going to the right side. As soon as he moved away from the center I recovered controls. Then, the ailerons hit their stops with him slightly past mid-wing!
I just couldn't hold him anymore (Maybe going a little faster would have helped)
So I banked hard right to flush him away.
That worked, he did his free fall, opened his chute and landed at the DZ with no issues.