I got the red triangle of death

My 2007 Prius has 195K miles on it. Tonight I backed out and the whip antenna hit the garage door. Seemed to trigger the red triangle of death, and some warning to put the car in park. It was a minute before I could start it, but everything seems OK for the time being.

Typically my car's state of charge goes from the 2nd green bar down two or three to the blue zone - or 65% to 50% according to Scangauge. Voltage varies from 11.9 to 13.9 typically - with the 2 volt jump when the ICE engages.

Hope it's the 12v battery or some one-time freakish event.