My first thought was dynamic rollover caused by a skid hanging up in something as they lifted off of the pad. This would be evidenced by the sudden pitch sideways witnesses report.

The spiraling towards the ground sounds more like loss of tail rotor authority, which could have happened (tr strike) as a result of the initial event, whatever that was.

Mechanical/engine failure seems like a pretty outside possibility considering the context. They had just landed, refueled, and were likely in a hurry to get back in the air.