Sounds subjective to me. Data abstraction is not a black-and-white binary property; it is a matter of shades of grey. Any abstraction hides some information and reveals others.
Another way to put it is that these two classes expose a different amount of functionality and make a different set of promises. So, what do you want the client to be aware of, and ...
Barbara Liskov has done research in the area of modularity:
A program is a collection of modules
Each module has an interface, described by a specification
A module’s implementation is correct if it meets the specification
A using module depends only on the specification
Modules provide the advantage of: