Yes, exactly. If I connect a physical loopback adapter to a network interface, I can't just ping any on-net address and expect a response. I need to add it as

Yes, exactly. If I connect a physical loopback adapter to a network interface, I can't just ping any on-net address and expect a response. I need to add it as an explicit interface address/alias first. Just because the packet loops back on the interface doesn't mean that it will then be treated as if it were addressed to the host. Linux special-cases 127/8 on the virtual loopback interface and will treat all looped-back packets as if they were addressed to the host, even when the destination isn't explicitly configured as an alias. This behavior is not required by the quote from RFC3330.