Here is what happened. I call this "Book Drop Debacle".
Note max speed recorded was only 16mph. (Maybe up to 20mph, since the camera seems to update once per second,)
I was in Hold mode, but because the chute is 1-foot shorter than it should be, and because I've curbed a rim before in this "bus stop" style book drop lane, I was very leery of staying away from the curb, too. So I leaned out the window to reach the chute, and the car suddenly took off like it was possessed. Apparently I pushed against the floorboard right where the accelerator pedal was.
About a $7000 lesson to put the trans in Park instead of using the Hold feature.