I'm glad I'm not the first to have spotted this. It seems to me that there is a problem with many of the audio recordings in this course that the speakers appear to assume the vowels in all stressed syllables should be pronounced long. I have reported this sentence as "The audio does not sound correct".
No, nothing is accusative in this sentence.
Notice that the verb is "est." With forms of "to be," you only ever use nominative case.
If the book is (or isn't) something ("A book is not a student"), the whole point of the sentence is to equate the two (or deny that the equation is correct).
(Think of it this way: "The book hits the student." There's an accusative in that sentence, because the book (subject) hits him , the direct object. Liber discipulum ferit. (ferio, ferire, to strike) )
A better sentence for understanding "is" would be: The student is/is not tired. (adj. "tired" is describing the subject, "student") Discipulus est (non est) defessus.
The book is / is not big. Liber est (non est) magnus.
(With "to be," everything is in the nominative case.)