Rationale for explicitly calling unshare(2) in child_fn after clone(2)

According to the man page of unshare(2), https://man7.org/linux/man-pages/man2/unshare.2.html

> CLONE_NEWNS: This flag has the same effect as the clone(2) CLONE_NEWNS flag.

May be a trivial question, but forgive me since I am new to this area.