I don’t get why everyone is so surprised. Cars aren’t meant to drive through standing water. The suspected depth is not an issue, since any water you can’t measure should be assumed to be too deep for your vehicle (Jeeps with snorkels aside).
It wasn’t a spray that Lillith encountered. It was certainly more akin to sticking the end of a Shop-Vac hose in a bucket of water. Except Shop-Vacs are meant to handle water ingestion. Internal combustion engines aren’t.
It wasn’t the fact that water is wet that killed the engine. It’s that water is incompressible. You could submerge the intake in motor oil or gasoline–things normally found in the engine–and the same thing would have happened. (Although the gasoline might cause other, secondary, issues.)
Some cars lend themselves to this kind of damage through their very design. Ten years ago, I had an older (mid-80s) Audi with a very poor intake location. The end of the hose was at axle level right behind the bumper. My dad (an Audi mechanic), cautioned me to avoid deep (and not-so-deep) water befcause he had seen quite a few 4000’s get hydrolocked. The OP’s Mini appears to share this very same design flaw.
Cars are often a lot tougher than people give them credit for. Cars are also sometimes a lot more fragile than people give them credit for. The problem is that the average driver usually doesn’t realize which is likely to be the case at the moment.