Sorry about your ESC, but I'm happy the plane survived.
There's a dozen different things that could have happened. One of the big electrolytic filter capacitors could have experienced a breakdown and shorted out. That would produce a lot of smoke! Or you could have had a power transistor (I think they are MOSFETs) burn up. It could be caused by bad design, bad component quality, sloppy manufacturing or just plain bad luck. Cheap stuff is more likely to burn up, since they design them with less margin and cheaper components than the expensive stuff (at least in theory).
Not much use in speculating what happened. If you want to prevent it from happening again, get an ESC that's about one size too "big". For example, if you know the max amp draw of your motor is 28A, don't get a 30A ESC, but get a 40A. The difference in price isn't that big.
You have about a zillion ESCs to choose from, but this one is cheap and people seem to be very happy with it: