2011 prostar wont turn over??

2011 international prostar with a cummins isx and a 13 speed eaton fuller.
I was in Texas rolling down I37 just past corpus cristi when I heard a noise kinda like dadadadadadadada. Not a knock from the engine kinda noise. Sound like it was coming from right under me. Let off the cruise was slowing down and all the sudden sound of something breaking. Engine shuts down clutch like sucked in a bit and was super spongy and I pushed it to the floor and it wouldn't let me take the shifter out of gear. Coasted to the shoulder. Stopped pulled with all my might and finally pulled the shifter out of gear. Smoke was coming from the inspection hole on the bell housing and there was some oil not a ton but some oil had been puked out of the crank case tube. Tried to turn the engine back on and it wouldn't turn over. It acted like it was being held back. Not a click noise but like it wanted to turn it but it was jammed.

Towed it to freightliner because that was the only shop willing to look at it. They turn the key look under the hood look under the truck say yep its seized.

I ended up sending another guy to look at the truck and he said he was able to turn it back and forth by hand. Well with tools pulling on the tools not actually by hand but you know what I mean. He said it felt like the cylinders may have been pressurized. Like a hydro lock.

Has anyone had a problem similar to this or have any idea what it may possibly be? Truck was running perfect up to this point.

 

Black and full. Wasn't milky at all.

 

I looked up through the inspection hole and the clutch looks perfectly fine....