(Edited out, as this might be user error. I’ll check further.)
(Edited again; this was user error but the user it not entirely to blame.)
In Webmin’s DNS module, the phrase “forward zone” is used with two meanings.
On the Webmin : Servers : DNS Server page, the link “Create forward zone” means forwarding name server, not a forward zone.
But on the Webmin : Servers : DNS Server : Create Master Zone page, “Zone type Forward” means a forward zone, not a forwarding name server.
I mistook one for the other. I have not seen "forward zone"refer to a forwarding name server before.