Don’t rule anything out. If you saw some of the crazy sh!t I saw flying in China you’d agree that just about any scenario is possible.
59 y.o. Captain gets hard terrain warning. Must be punished. Downgraded to FO as he approaches retirement. Gets rostered with a leader captains (who downgraded him) son. Makes for an interesting cockpit dynamic. Who’s really in control in that situation? Anyone who’s flown in China knows it’s not the guy in the LHS. Up there it doesn’t matter a damn what’s right, it’s all about who’s right. Add in lots of hands on the controls, (a staple in Chinese aviation) and it doesn’t take much to create a disaster.
Might have just been the cranky old guy giving the yoke a shake to make a point, or stomping on the rudder (yup, seen that happen), with zero regard for consequences. Engine failure and stall also a possibility, keeping in mind that if you let a yaw develop in to a roll, it will eventually lead to aerobatics if left unattended.
Saying aviation in China is much safer than it used to be is like saying wars aren’t as messy as they used to be. The weapons may have changed but it’s the same result in the end.