Yes, single pole is the important part, it means there are _not_ two separate circuits with a common neutral as we suspected before, but a single circuit for both the disposal (through a switch) and dishwasher.
Just to confirm, neither the dishwasher nor the disposal (when switched on) run when that one breaker is off but all other breakers are on, yes?
I'm scratching my head, I suppose an open neutral could have sent all the dishwasher's return current through the disposal's housing through the ground connection, causing it to heat up...