As illustrated in your photograph, the iPad has bent at the weakest and most vulnerable point of the chassis structure - this being the location of the edge-mounted smart connector.
Damage of this nature is characteristic of physical/mechanical force being applied, often as a consequence of being carried in a backpack or bag with other items - or, commonly, being placed on soft furnishings or a bed and being accidentally sat upon. Overheating cannot cause this type of damage.
In some situations, placing the iPad within some tightly fitting cases can require “some persuasion” - leading to unintended (and perhaps unnoticed) consequences. Some models of iPad are particularly vulnerable to this type of damage.
Many cases provide good protection from accidental drops and scratches - but only a few have a rigid back that provides significant protection from unintentional bending. Those that do provide mechanical protection often have a solid polycarbonate backplate - with a TPU (synthetic rubber) surround. Many have a similarly semi-rigid flap-cover that provides screen protection when the iPad is not being used.
Given that the illustrated damage is unlikely to be accepted as a warranty issue, repair will be expensive - Apple’s flat-rate being c.60% of the “as new” cost of the iPad. You can verify the repair cost for your country/region here:
iPad Repair & Service - Apple Support
For eligible devices, Apple generally offer an exchange - whereby an iPad, in lieu of a repair and for the same cost, is exchanged for a renewed/reconditioned device of the same model and specification.
If you have benefit of an active AppleCare+ plan, you can have your iPad repaired/replaced. As AppleCare+ is an insurance product, there will be a small excess/deductible fee to pay.
