The existence of an IPv6 interface does not necessarily mean the system is using IPv6. The interface is not brought up until you actually configure an IPv6 address on that interface.
For example, the following output of the ifconfig command shows that the inet6 net0 interface has not been marked as UP and has an address of ::/0,meaning an IPv6 interface is not configured.
# ifconfig net0 inet6 net0: flags=120002000840<RUNNING,MULTICAST,IPv6,PHYSRUNNING> mtu 1500 index 2 inet6 ::/0
The in.ndpd daemon still runs on the system but does not operate on any IP interfaces that do not have an addrconf address configured.