I just probably found what DuckieTigger had in mind:
Unsuccessful teardown
Seems bad. Probably well planned lifetime

Or maybe just very bad disassembly, because it looks like batery exploded inside device itself.
I wonder why iFixit did not do any teardown, they are often very good at these things. And when only option to take apart that thing is destruction, they just give it garbage score...
Update: Just posted
question on iFixit, let's see what happens, or maybe add some votes if you are interested too.