I think you are not mixing things here.
From LSP:
Liskov's notion of a behavioral subtype defines a notion of
substitutability for mutable objects; that is, if S is a subtype of T,
then objects of type T in a program may be replaced with objects of
type S without altering any of the desirable properties of that
program (e.g., correctness).
LSP refers to subclasses.
List is an interface not a superclass. It specifies a list of methods that a class provides. But the relationship is not coupled as with a parent class. The fact that class A and class B implement the same interface, does not guarantee anything about the behavior of these classes. One implementation could always return true and the other throw an exception or always return false or whatever but both adhere to the interface as they implement the methods of the interface so the caller can call the method on the object.
