If you have the "Remote-AP Backup" enabled in the enet profile of that ethernet port:
The client traffic will survive, regardless of how the wired profile was configured when connected to the controller. When the AP is coming up, before it connects to the controller, if remote-ap backup is configured, it will automatically give a client an ip address out of its pool in the ap system profile and source-nat all traffic out. Even if the client is hardcoded with an address that does not match that pool, it will source nat all of its traffic out with no ACL.
Long story short, with that parameter enabled, it does not matter what ip address the wired client has. If the access point is up, and has an ip address, but cannot contact the controller, it will source-nat and forward all wired client traffic out of its routed interface. Many times there is a switch between the wired client and RAP, so the client does not "see" the interface go down and retains its existing wired ip address. That traffic will be forwarded out of the RAP to the internet.
The idea is to allow any wired device access to the internet, even though the AP does not have connectivity to the controller. It would be for devices that need internet connectivity, even though the controller is down.