It's an opinion, there is not Bitcoin Webster's dictionary
Discussion
Most would say a layer is an abstraction of another layer, since ecash is an abstraction of layer 2 lightning, it's a layer 3.
Where did you get "most" from?
Networking
From a networking perspevtibe this is very true, and aids confusion - The way I see protocols wrapped in protocols, ecash is a layer 3 regardless of its properties in relation to whichever protocols its wrapped under, i.e, as a Bitcoiner it matters whether I can trustlessly settle back on-chain, but from a networking and protocol perspective it's the relation between the protocols and how they intertwine that matters, i.e How can two languages interact for the same purpose, how does one carry the other.