Talk to a true, old-time steamfitter sometime. (Preferably before they're all gone.)
You can heat a sealed container of water to far above water's unpressurized boiling point, without it technically boiling. You end up with a container of very hot, supersaturated steam- that is, a fluid that is neither steam nor water.
The trick is, the only thing keeping it in that state, is the pressure. If the pressure containment is lost- even by a relatively small amount- the supersaturated fluid flashes to true steam (since it's far above the boiling point of water) and you get a massive increase in volume.
That increase in volume- which happens nearly instantly- brings with it a massive spike in pressure as well. Meaning a loss of pressure can indeed lead to an essentially explosive increase in pressure.
It used to be sadly all to common back in the early days of the industrial revolution, when steam boilers and steam engines were the sole source of motivational power for entire factories. There's a huge amount of actually surprisingly sophisticated technology behind being able to safely vent off steam pressure (IE, into a steam turbine or a steam engine) without causing a catastrophic explosion.
Nine times out of ten, if you heard of a "boiler explosion" at a plant back in those days, it wasn't due to an overheated boiler, it was due to a broken pipe or failed seal that caused a loss of pressure.
Yes, the rest of the description of Doc's coffeemaker is just a tad farcical (based off of the "light gas gun" concept) but the steam physics are genuine.