A single pilot might leave the cabin of a running helicopter for many reasons. The techniques to do so were routinely covered in the primary phase of the US Army when I taught there some 40+ years ago. Yes, the occasional training aircraft mishap occurred without crew at the controls. The most memorable was the solo student whose aircraft fell off a pinnacle, a second solo student landed, unaware, exited the aircraft, and then watched his aircraft fly away with the first student at the controls.
Some operators permit it, some don't, but it's not unusual that it be allowed here in the former colonies. My present employer currently allows AS350 drivers leaving the controls in certain conditions: stable on the deck; ground idle; collective down and locked (never had the collective rise with full hydraulics, but have seen some cyclic motoring); and cyclic friction firmly set; autopilot off. I don't think an Astar would lift at ground idle without a pretty stiff breeze (Edit- Alouette3 posting shows me in error). But inadequate cyclic friction, motoring and/or an unlocked collective might generate enough force at flight idle to unsettle the aircraft, perhaps lift it, and what scares me most- tip the disk presenting a hazard even if the aircraft itself doesn't move.
I've never flown for Papillion and don't fly AS350B3 or left hand pilot seat. Does the B3 normally shutdown from flight idle? That might accustom pilots to ground ops with full NR. Is the collective lock less positive than other 350 types? The collective lock on a left-hander would be in a high traffic area.