Ahh I got to recovery!! (and figured out how to power off the device in the previous state - just keep holding the power button and ignore the fact the screen doesn't go blank!)
I read through the thread again - my boot was also set to slot b, same as ardy!
I did this:
Code:
fastboot --set-active=a
Setting current slot to 'a' OKAY [ 0.011s]
Finished. Total time: 0.013s
fastboot reboot recovery
Rebooting into recovery OKAY [ 0.008s]
Finished. Total time: 0.108s
It's factory resetting now.