Thanks for using hcm. It is unlikely that your grandfather is suffering from ulcerative colitis
unless he is already a know case. Bleeding from rectum
can be caused by a mass or polyp or hemorrhoids(piles). He needs to undergo per rectal examination
to determine the cause. Hence i advise you to go to a local surgeon who can examine and if required he will order for furthur investigation like colonoscopy
. If it was a onetime symptom and does not recur anytime in the future you can ignore this and not worry about it.