You are correct, re-baptism is never to take place. If someone is validly baptized that means the sacrament has left a indelible mark on their soul, nothing removes it. Once baptized, always baptized.
The only time a “re-baptism” would occur is what is called a conditional baptism. This only takes place if there is serious reason to doubt the validity of the first baptism. In the case you describe the baptism was obviously valid and therefore cannot be repeated.
