People from Weibo says it is used to cue entangled rope. After seeing a video of a cargo plane crashing into the ground due to entangled ropes when dropping military equipment, I must say this role is very important, there is no chance of survival if anything that was supped to drop out of the cargo bay gets stuck due to entangled rope, you plane will most likely go nose dive into the ground.I don't know but I guesss:
If it is not a hook to hold something from going out, it could be a pusher. I imagine that the cargo would normally slid out by gravity, that needs the aircraft flying slightly head up. But if the wind/altitude/turbulance situation force the aircraft not to provide enough angle for a moment, one may have to give a little push.
Another possibility is that it is blade to cut entangled rope. Heavy cargo are usually pulled out of the hold by deploying a small parachute. The rope of it can get entangled with protrusions of the plane. A blade on a long pole can get rid of the cargo and clear the way.
The length and the shape of this thing is perfect for reaching out and cut rope, a simple pull will easily cut off any entangled ropes and free the plane from a inevitable death when heavy cargo gets entangled.