I missed the following section on my first read of the report
"The operator inserted a 300 ft line into a hi-line bag that was advertised as either a stand-alone
item, or fitted with a 75 ft line. In addition, the hi-line bag was a sausage shaped bag with a narrow
throat relative to the amount of line inserted. Therefore, when assembled, the hi-line equipment
presented an increased risk for restrictions during a hi-line evolution and the equipment was no
longer fit-for-purpose."
But this doesn't explain the recoil from a wire that should have only been exposed to around 40kgs of tension..