Being a bit of a electronics technician, from what it looks like to me (personal opinion) someone sat on it on a soft surface or an animal of some kind. Battery damage would show different signs, good luck getting it replaced.
Typically with battery swelling (and the fact that the damage is on the opposite side of where the battery is located) you'd get some kind of mild odor when your face was closer to the ipad, especially since there's a direct open space. A long with such, you'd see more of a warping then a bend. (Think of something large pushing out of the easiest place on your iPad. The aluminum back is not the easiest place to push compared to the non-screwed in glass.
Also, from my knowledge there wouldn't be any graphical issues on the front of the screen, as the screen would have pushed upwards not the aluminum, and only minor pushing of the logic board would actually happen.
Don't take my words for it as I have not actually looked at an iPad internally.. just from pictures.
UPDATE:
I think I've actually figured it out by looking at your pictures.
From what it looks like and from experience with similar damage on electronics, it looks exactly like someone leaned on it with their arm on a bed/soft surface. I retract my animal/sitting statement.
The even pressure wouldn't cause the screen to crack but the aluminum would bend if the person did not notice they were leaning on it for a decent amount of time (5-15 minutes).
Could have happened by complete accident. Let's say where you charge the iPad is close to your bed. You place the iPad on the bed to charge for the night, forgetting about it an making your bed. Leaning on the bed for a bit to find the iPad for several minutes and then placing it on a desk to charge overnight would cause almost exact damage to the device as the pictures depict.
Typically with battery swelling (and the fact that the damage is on the opposite side of where the battery is located) you'd get some kind of mild odor when your face was closer to the ipad, especially since there's a direct open space. A long with such, you'd see more of a warping then a bend. (Think of something large pushing out of the easiest place on your iPad. The aluminum back is not the easiest place to push compared to the non-screwed in glass.
Also, from my knowledge there wouldn't be any graphical issues on the front of the screen, as the screen would have pushed upwards not the aluminum, and only minor pushing of the logic board would actually happen.
Don't take my words for it as I have not actually looked at an iPad internally.. just from pictures.
UPDATE:
I think I've actually figured it out by looking at your pictures.
From what it looks like and from experience with similar damage on electronics, it looks exactly like someone leaned on it with their arm on a bed/soft surface. I retract my animal/sitting statement.
The even pressure wouldn't cause the screen to crack but the aluminum would bend if the person did not notice they were leaning on it for a decent amount of time (5-15 minutes).
Could have happened by complete accident. Let's say where you charge the iPad is close to your bed. You place the iPad on the bed to charge for the night, forgetting about it an making your bed. Leaning on the bed for a bit to find the iPad for several minutes and then placing it on a desk to charge overnight would cause almost exact damage to the device as the pictures depict.