ipv6 is not completely disabled on the interfaces
When IPv6 Configuration Type is None on Interfaces configuration page, IPv6 link-local addresses still uses
You can see OSPFv3 hello packets, can use ipv6 from these interfaces,
or, if rules like "IPv4+IPv6" used, can connect to services
to completely disable IPv6 on interfaces, option ifdisabled must be used, i.e. "ifconfig vtnet0 inet6 ifdisabled"
from ifconfig (8):
ifdisabled Set a flag to disable all of IPv6 network communications on the specified interface. Note that if there are already configured IPv6 addresses on that interface, all of them are marked as "tentative" and DAD will be performed when this flag is cleared.