Your definitions are correct.
As to the dynamics I haven't a clue. In simple tin tops understeer can be caused by too much spring on the front and or too little spring on the rear, whilst oversteer is generally due to the rear end being set up too hard.
Then you get ride height which also needs to be factored in.
Then again either condition can be caused by the driver. F'rinstance if you go too deep into a corner then apply the brakes, you'll induce oversteer because the car is already turning as you hit the brakes. This technique is employed by racers of front drive cars.
OTOH if you fail to slow the car before turning in then you'll get understeer which from experience soon has you heading for the scene of the accident.
Now, you mentioned JV so I suspect its driver induced.
BTW. If you scroll down to related threads you'll find at least one topic discussing this.