I think my ex is managing to fool his parents to a large degree.
He can do this even more easily as they live abroad- and he’s just told them his version. He was a challenging child ( he stole money from them- I found out too late! ), but he’s probably made them believe he’s a changed adult, and they probably don’t want to admit he may not have done.
His mum shouldn’t have spoken to you. It must be upsetting. But just ignore it. You know the truth.