It is abstract. Right and wrong do not have a physical presence out in the world. They are universal human concepts that we hold inside our minds. And not only that, but many other mammalian species also have a concept of right and wrong. They too are able to abstract.
Labeling behavior is also an abstract operation of the mind. Dr. Lewis's entire career (and this would be true of many scientists and doctors) involves the use of abstractions. Such as the concept of "mind" or "psyche" or the concepts held true inside psychiatry (where of course there is much debate over whose abstractions are correct).
So, Dr Lewis should be comfortable using "abstractions" as well known and universal as right and wrong.
IMO.