What was his stool like? Was he somewhat constipated? If he was it may have been uncomfortable to poo because it was too solid or something. And if it was readlly solid and he tried to pass some that was to big he could have made a little tear around the hole and caused it to bled. I know that happened when with Brayden when he got constipated from the change to formula..

I would definately mention it tho