clarification/possible typo in "Pool options" under nat/port forwarding?

[kensan]

Here https://docs.opnsense.org/manual/nat.html#some-terms-explained one can read the following :

Pool options: When there are multiple IPs to choose from, this option will allow regulating which IP gets used. The default, Round Robin, will simply distribute packets to one server after the other. If you only have one **external IP**, this option has no effect.

though It makes perfect sense for outgoing nat as one can have multiple external ips to nat from to.
I'm interested in the option in the context of port forwarding as it is in the UI for port forwarding (and I didn't test it to so what it really does).
When in the context for port forwarding the implication is that  someone or something tried to connect (external_ip:external_port), how does the  above **external IP ** square with this scenario? Internal IP makes more sense as on can have a plethora of internal IPs to forward to.
Or am I missing something here?

If it is indeed the case, doesn't his make relayd redundant?