This lady is slap full of positive ju-ju. She had it fixed pronto. Chain looked fine/ok and sprokets good, no worn or missing teeth. Possibly loose,loaded bike bouncy roads. Happened at zero speed. Best I could tell.
Hope you don't mind me answering for you, but I know you're back in the sticks for a bit.
Glad you stayed dry, it was a gully washer around here. All those gravel roads near you are usually better after a little rain anyways. Enjoy!