Bangle2 died on low power - did not shut itself down?

I did not constantly monitor the screen but just noted that after 2-3mins it was ok again. I did not do anything on the watch in that few minutes (no screen touch or button press).

My assumption is that because of the low power something did not correctly work/communicate anymore, probably as you said "just" the communication to the screen.
And when the backlight was off and the battery could recover for a short time again, maybe it just raised the power enough to pull off a full redraw again.
Yes, this has never happened to me before but usually I also don't allow the battery charge to go below 10%. Just this time I completely forgot.