Not all that weird for a battery to get so hot that it can cause severe burn temperature wise and chemical burn from leaking electrolyte. This happens when the battery terminals are shorted or/and are installed in reverse direction.

I know that lithium ion batteries carry something like 10% of energy in gasoline for the same volume. And gasoline doesn't even carry its own oxidizer. Put it another way, that small battery can heat a mug of water as much as burning a two tablespoon full of gasoline.

NimH battery is only as third as powerful as lithium battery but still think of burning two teaspoon of gasoline.

And yes batteries can explode or catch on fire if there is uncontrolled reaction. This occurs when battery terminals are shorted.

You did the right thing by tossing it outside. Hope you or someone went to retrieve the dead battery. If not please do so. The leaking electrolyte is very bad for the environment not to mention hazard to anyone who comes in contact.