Most likely they did not clean the oil out of the IC so it ran away and blew up when it ran out of oil. Most likely a rod exited the block.
The oil was from the bad turbo that got replaced. The new one blew up the motor because it could spit the residual oil out of the intercooler into the intake. The new turbo is likely just fine unless it got FODed. Pull the pan. You will get an education. Don't be so sure the motor is not ventilated. When I pulled the turbo off this 2003 NB that is my latest project, I could look in and see the crank. No holes were visible before that. I will post pictures when I get it out.