I think you can say that a simple on chain element to a protocol doesn't make it, itself, into a layer 2, such as fidelity bonds on nokyc markets, or any type of protocol that needs objective timestamps, but rather whether it routinely reads and writes data to the chain, read only most of the time doesn't really make it a layer 2.

I'd say the distinction is more about where the bulk of payment activity occurs in the protocol. If it's primarily transacting on LN then it's layer 3.