You’d have to ask a physicist. I would be surprised if you couldn’t make other liquids “wet”. The solid analogy helps with conceptualising an interface, one material on another. I suppose you could make water wet, by freezing a block and then splashing said block with water but that doesn’t equate to it being wet itself, if that makes sense.
It threw me at first too. Helps to think of it as wetness being an interaction between a liquid and solid. Water makes things wet, it isn’t itself wet.