If the translation of the instructions is correct then it states:
Open the aircraft ramp and make sure that it doesn't move.
Make sure that there are no people/vehicles/obstacles 5 meters from the ramp
Via the ACE interaction menu with C-130J, unload the vehicle (the action can be canceled), remember that when unloading and landing, the principle of last in - first out
So as I was following the instructions, I opened the ramp and BOOM.
Also this wasn't the first time it happened, as I was flying the first round to north with some infantry and one humvee with 50cal, the humvee decided that it will unload itself mid-flight, thus we were not able to paradrop it. After we landed on the spawn airfield the humvee was unloaded and FREELY moving inside the C-130J, as we were scared to do drive it out, I just loaded and unloaded it again, but then I wasn't able to get in the humvee and drive it somewhere safe, so @Palalalasaur had to get in it and drive it off the runway, but then he wasn't able to get out of the humvee, so I had to go to him and get him out of the damn humvee via ACE.
Screenshot of the damn humvee loaded inside (pretty sure that isn't correct)
So if you are calling the all above MY mistake then you are a madman.