What can one damage by bending the wheel? What parts may be damaged by bending rear wheel manually with very high force?

My father bent rear wheel several times with such high force that the tire contacted the seat stays. Could he have damaged or worsen any part of the wheel (hub, hub axis, bearings, spokdes, etc)?

I complained about the way of transporting my bike in his car (lying horizontally on rear wheel) so he tried to prove there is no influence on wheel centering and hub health.

Is it okay that the wheel can be bent slightly with proportionally high force?

Bike model: Author Codex 2015, wheels: Author Radon, unsure about type of the hub.
There is probably no damage.

In wheel-building, one of the ways to relieve torsional stresses in the spokes is to lay the wheel flat on the ground, so that it rests on the hub. While you press the rim on the ground at the 6 o'clock position by your knees, you put all your upper weight via both arms on the rim at about the 10 and 2 o'clock positions. You feel the elastic deflection, which depending on spoke tension and number may be about 1 cm. The spokes on the de-stressed side are able to unwind the torsional stresses. You rotate the wheel in small steps on both sides. There is no damage to either rim or hub.

Look how this process was cleverly implemented on a luxurious wheel truing stand (at about 2:10) 
                
            

As long as you keep within the elastic deformation range, there is no damage. The characteristic of the elastic range is that the wheel returns to its original shape if the force is removed.