So you can opt out or in to syntactic sugar, that makes C++ an interesting and useful language, but how you implement OOP, doesn't really affect if it is OOP.
You can implement OOP in C if you do vtables for inheritance hierarchies manually, among other things, but that is different than what Linux does.
It's a function belonging to an object, to which is dynamically dispatched with something I would call a vtable. To me that sounds like a classic example of OOP.
Data abstraction is a core of OOP.
This pattern can be used to implement inheritance, when it isn't here that doesn't mean its not OOP.
> Object-oriented programming (OOP) is a programming paradigm based on the object – a software entity that encapsulates data and function(s). An OOP computer program consists of objects that interact with one another. A programming language that provides OOP features is classified as an OOP language [...]
You don't disagree, that this kernel pattern is about data abstraction. You probably don't disagree, that the kernel uses functions. The kernel uses "objects" (FS implementations) that follow a defined set of functions, sometimes called "class" (vtables/wtables/however you like to call them). Therefore I conclude what the kernel does here is a prime example of OOP.
I know ADT and OOP are different concepts, in another answer I wrote what I think the base differences are. But they are related, and in the definitions I am familiar with, ADTs are a base concept for OOP. And OOP can be an implementation for ADTs.
If you don't think the implementations I provide are enough to apply to the kernel, can maybe provide your own definition according to which we can evaluate this, because I feel like we are beating around the bush. But please not something that says this can only be happening in an OOP language, to these I would plainly disagree with, because OOP is a paradigm and not a property of a language.