Had to Reset my 2010 by disconnecting battery

My 2010 Prius is garage kept and I haven't taken it out in over a week due to the snow. I use my older Prius for that.

Anyway, this morning was sunny but cold so i decided to take the 2010 for a spin to work. Well when I got in to the 2010, pressed the break pedal then the start button, the dash came on but no Toyota welcome. And the car did not start. There was a yellow triangle on the upper dash to the right.

Then I tried turning off the car, but it would not turn off either. I tried this cycle, for a while to no avail. So I decided that the battery must need a boost. But that too did nothing to change my situation.

Finally i disconnected the positive contact on the battery and reconnected after about a minute. The car then started without issue. I turned it on-off a few times and all seems fine. So I just took it to work.

Has anyone experienced this before in a 2010 Prius? Or have any idea why the system needed a hard reboot????