As already commented by KiltedTim, iPads do not spontaneously bend. As illustrated, the iPad chassis has likely been physically stressed beyond its design capability - and the casing has deformed due to this pressure. The most common explanation is that the iPad while placed on a soft surface has been sat-on. Even a good case will not necessarily protect the iPad in such circumstances.
If you have benefit of an active AppleCare+ plan for your iPad, you may be able to make a claim for damage. If applicable, for the cost of the levied deductible/excess fee, the iPad will be exchanged for a reconditioned iPad of the same model and specification.
Otherwise, some anecdotal reports suggest placing the iPad on a flat surface, with another flat object (larger than the iPad screen itself) on top of the iPad - and then adding some additional weight (such as some books) on top of that, leaving the iPad undisturbed overnight. It is claimed that the iPad chassis may be somewhat straightened. Of course, should you choose to do so, this will be entirely at your own risk.