The thick black exhaust is partially combusted diesel fuel (a little too rich). The thick white exhaust is uncombusted diesel fuel (way too rich). I suspect these didn’t have anything to do with the failure but rather some issues with their tune. Catastrophic block failure like that happens when the block twists. Like when you wring out a towel and twist it but with a much smaller twist.
If you imagine a power drill in your hands with a hole saw, think about the force you feel in your hands, and how much effort it takes to keep the drill in place and not twist out of your hands. The drill is the engine block in this case. The job of the block is to keep the crankshaft and pistons in place (among other rotating bits). The tolerances for everything to work right are very small. When the block twists the shapes change from perfectly round to ever so slightly oblong. Even the slightest change is enough to seize the pistons.
When the pistons seize in the oblong cylinders the crankshaft is still spinning along with the rest of the drivetrain behind it. All of the connecting rods break and some or all of those will break through the block. Everything in the block at that point can potentially come out (oil, fuel, combustion, coolant, etc.). The amount it has to twist for this to happen is extraordinarily small.
This is the only failure mode that makes sense given the extent of the failure. Other issues with coolant or lubrication might affect a single piston. You’d get smoke, maybe some fire, lots of noise and small parts coming out but not the block leaving the engine bay. It comes with the territory when you try to get 9 or 10 times as much power out of an engine block compared to what it was designed for.