Although he is free to dispute the comment, the reality is that the comment does not affect his credit score and won't affect his ability to obtain financing for a car or a home.
Hope this perspective helps!
I agree that you should have him dispute the comment but since it is true and verifiable I suspect they will not remove it. It is also probably true that his credit will not be affected by your bankruptcy. The comment is there to show that co-debtor (you) are bankrupt and your son is therefore solely responsible for the debt.