The difference that make, when the IMU is off closely to half a turn (180 degrees) is that the AC will flyaway in a straight path ... what the craft think's is the front is actually the rear.Wow, IMU Yaw off by 127 degrees is huge and makes a heck of a difference.
If close to 90 degrees off the AC instead will flyaway in a circular path (known as a toilet bowled path).
Your friends flyaway path looked to be mainly straight ... so I imagine the IMU was off closer to 180 degrees due to the earlier mentioned 2 reasons ... only the DAT log can specify which of them actually caused this. One is definitely a pilot error & one isn't.