The formerly blind man proclaimed on how he was healed to the Pharisees. But then the Judean people doubted that the formerly blind man was blind in the first place! They went to the blind man's parents and asked them if the seeing man was the blind man.
The parents did confirm that the son the peeps were referring to was the parent's son. However, the parents told them that they don't know the son's current seeing capabilities or who healed the eyes and told them to ask the formerly blind man (9:21,23). We know that part of the comment phrasing is because the parents knew that confessing that Jesus was Christ means getting kicked out of the synagogue (9:22). Considering the priority the synagogue has in Jewish life, getting kicked out was a big deal. The parents were likely worried about their reputation. Even today, fear of maintaining reputation may be part of the reason why people may not speak on Jesus or even the truth.