I wouldn't base a thesis on his theory though.
Auto's are popular with plenty of people and are getting a lot more represented on the roads.
A lot of those people don't have a lot of experience driving long distance on corrugated roads.
They are more likely to be mounted in the more comfortable vehicles than your average workhorse.
Most of the locals that have drive the road regularly would have manual cruisers because they don't shake to bits and would probably be under represented.
But I don't think the issue is the auto. If I'm belting down the road in top gear and have to brake heavily, I'm generally more concerned with braking, steering and not hitting the obstacle to worry about down shifting right away. I generally get my gear changes out of the way before the corner. Modern autos will down shift when you brake anyway.
I think the issue is more that the vehicle is comfortable, so they carry too much speed into the corner. Mid corner corrugations throw them off line, panic braking or an over correction (or both) and they are on their roof.
Speed and inexperience would be more of cause. I doubt the transmission is a significant contributing factor.