Lost power in reverse

Today I was backing out of my garage and onto a near level driveway when my 2006 I-tech prius lost power - it died.
I was travelling at about 4-5 km/hr at the time when the system seemed to shut down. By the time I realised something was wrong, the car was slowly rolling to a stop, and looked at the instrumentation only the gear layout was showing with the "B" part missing.
I applied the brakes and pushed the power button and the instrument panel lit up as normal and I continued backing out onto the street.
One thing I should mention, the failure happened about the time I pressed the button on a remote door shutting device. Initially I wondered whether or not I pressed the power button instead of the remote (which is velcroed to the diver's door window sill not far from the power button). I cannot remember if the door was still open but I don't think so.
Later on, I tried to duplicate what I may or may not have done but could not get it to fail again, even by pushing the power button.
Anyone any thoughts on this one?

 

Hi donne, no I am sure I did not bump the gear lever into neutral. I use the rear view camera and two side mirrors to back out of my driveway and it is not until I get to the gate that I swivel the head. Having said that, I will try putting it in neutral tomorrow and see what happens.
Even so, how would selecting neutral power down the car?

 

The device is a small hand held remote control with only one button to open or close the garage roller door. It has a range of about 20 m.
I have been using it in the Prius for 2.5 years without any problems.

 

I hope you are right, Richard. I would rather it be me that failed than my beloved Prius.
Any idea what I might have done wrong?

 

Thanks for the comments, guys.
To start with, I believe the scan gauge will not work in an Australian Prius.
Bob64,
Unfortuneately, I cannot go along with your suggestion as to what happened.
I can leave my car in neutral at any point in the garage or driveway and it will not roll backwards or forwards. I must have had power to travel the 3-4 car lengths at 4-5 k/hr before I noticed a loss of power.
However, I could have hit the power button instead of the remote door shutter without the brake being applied. I have since tried this and it did not shut the Prius down. I certainly did not select neutral but after I discovered the failure I did put my foot on the brake and hit the power button to get going again.

 

I guess anything is possible but I don't see how I could have shifted into neutral.
Remembering our Prius is right hand drive, I would have had my right hand off the steering wheel to activate the roller door remote control (it resides on the right hand door sill) as I cleared the door. The drive selector is on the left hand side and the only way I could select neutral is by hand - my knee will not reach the lever. I need at leaset one hand on the wheel to make a small adjustment in direction as I back out of the garage.
Also. going into neutral would not power down the car. The parking pall did not engage and I would have thought it would if I were in neutral and powered down.
I must admit that I did think I may have knocked the selector after selecting reverse and starting to accelerate out of the Garage and then pressing the power button instead of the door remote. When I tried to duplicate the problem, I found that the lever has to be held in neutral for about 1 second and pressing the power button while still rolling did not power down the car.
We do have a ghost like figure that lives with us who we have named John (at least two people have seen him) but he has never worried us before. Perhaps he was playing silly buggers with me!