The report is pretty vague on details and it makes me wonder if it wasn't the coupling that exploded and not the hydraulic motor itself.
If there were issues in the hydraulic system, it is possible that any kind of rendering relief valve fitted to protect the motor may have failed.
It is also possible that the slipping clutch designed to protect the motor (if fitted ) was seized or had been adjusted to a higher torque limit in order to force more power out of the motor. After few burned out motors and coupling failures while lifting anchors it became mandatory, as part of the planned maintenance program of one fleet I worked in, to verify that the clutch was set correctly. This became a bit of an issue on some older boats when it came time to finding the fulcrum arm and counter weight used to set the slipping torque on clutch, either they we painted or rusted to the bulkhead or missing all together.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"