After overheating and headgasket change just 100psi compression - no start

A friend of mine had bad luck with his K30. The lower radiator hose blew apart and he lost all his coolant and overheated the engine because he didn't notice it fast enough. As he wanted to pull to the side it already was too late and the motor started to die and stopped running.

He got towed home.

Arriving at home he backed the truck into his garage (it ran again but very very rough).

He then changed the headgasket and hose with another friend (so I don't know what they did exactly) - and now it won't start at all.
Today I was at his place. We did a compression test and all tested cylinders show around 100-170 psi No wonder it will not start...

Has anyone a idea what could cause this? Is there something they could have done wrong or is the motor toast (rings/cyl walls)?
Some more infos:
* If I put my hands over the crankcase vent and oil fill it builds up pressure very quick
* It does not start with ether
* No pressure in the cooling system while extensive cranking
* They didn't machine the cyl. head, just cleaned it by hand


Thanks in advance.
Chris

Did they look at the cylinder walls to see if the piston scored them?

He said his friend told him they looked ok.

I’d bet with such low numbers the pistons swelled up and ate into the cylinder walls, and now that it’s cold it can’t make enough to fire. You can plug in a block heater and see if it will fire then.

if there was no marks on the walls, the rings collasped.

But how could it run to back it into his garage (it was cold by then)? Is there anything that could have gone wrong with the head gasket change? I mean...all points to pistons/rings because of the blowby, but...
I'm not familiar with 6.2 heads.