CM870 Burned piston

[Hemiterry]

I have an 2006 International 5600 dump truck with a CM870. Last week it died on me while idling and my mechanic found two leaking injectors and a worn gear pump. I had him replace the gear pump and all the injectors while he was in there. I picked up the truck and went straight to the gravel pit and got loaded with 15 tons of gravel. The truck ran great until I pulled out onto the highway which was at a steep incline. It immediately started running rough and barely had enough power to get up the hill to a place where I could pull over and get out of the road. After I got stopped the truck died and was spewing coolant out the cap and was at 230 degrees. I had it hauled back to the shop and they discovered the engine wouldn’t bar over. They pulled the valve train and removed the injectors and discovered #1 cylinder piston had a hole in it and was seized. They’re thinking the new injector is bad and was over fueling the cylinder causing the burned piston. They’re sending it to an independent lab to be tested. The injectors came from FleetPride but were not Cummins OEM. I don’t know what brand they are yet but I’ll find out. Does all of this sound legit and if the injector isn’t defective could it be improper installation or adjustment on the mechanics part ? Any input would be appreciated.