I disagree. It appears it occurred to someone (the jump seat pilot) pretty quickly that it was a runaway. They got pitch under control and hit the cutouts. My guess is they re-enabled stab trim in a troubleshooting / curiosity activity (lets see if its still doing it?) because clearly they did not need the electric trim to fly the plane.
Possibly they were trying to understand the (changed) function of the cutout switches:
"I thought the right switch killed auto but allowed manual electric trim"
tries various combinations of switch positions, ending with both up..
"There it goes again"
"That's strange, I have the conversion notes in my carry on, let me go get them"