i have 2 exodon tanks (i had 3 but im down to 2 now. all 3 can probably be found on youtube)
its no miracle. if you know what youre doing, its pretty easy to keep certain tank mates.
ottos and corys (along with fire tetras, and a couple of other fish) are gathered in the same places as exodons and they live together just fine in the wild. and if you do it properly, they can be kept in a captive environment as well.
of course, if you were to just drop an otto or cory in an exodon tank, it would either be eaten, killed, or stredded to death. certain precautions need to be taken when attempting an community with exodons. but its definitely possible.