Toddler questions

I was babysitting today and the little boy (4 yrs old) went poopoo and asked me to wipe him when he was done. I did, and we washed our hands and went back into the living room and I said "alright, lets play" but he just looked at me and said "my butt still hurts." I had no idea what to do, so I said, "do you think it needs to be wiped again, maybe it didn't get clean?" And he nodded and we repeated the process. He said it still hurt after that, and I told him to just wait and play a little while and see if if still hurt later. I guess it got better or he forgot, but what might have been the problem? Also, how would you handle that? So I know for the future. Thanks in advance!