Without speculating on how the crankarm got that way, I'm inclined to say that it has reached the end of its safe useful life. Especially that damage about an inch away from the pedal eye, that's a high-stress location and a common place for cracks to propagate and breakage to occur.
I did enjoy trying to identify (unsuccessfully) the service manual in the background. Looks like '90s technology for emissions controls but includes OBDII codes so probably post 1995.......
Last edited by daka; 02-06-23 at 02:26 PM.