what you are referring to could be a skin tag or hemorrhoids.
skin tag is a small piece of skin tissue.
the small surgery would be done to take this out.
i dnt see a reason why you should worry about this.
however to be sure it is just a skin tag and not hemorrhoids it would be better you get the discharge summary copy from the doctor who treated your son.
do have a regular follw up with your pediatrician
as it is difficult to say what your son had exactly without examining him.
i hope i have answered your query.