To be up to scratch means to be as good as what is expected, and in this context it is expected that he is knowledgeable and competent in Egyptian, but he is not.
Consider the staetement "Anyway, being a Babylonian with very little secondary education, he wasn't knowledgeable or competent enough in Egyptian.". Based on this statement, is "Anyway, being a Babylonian with very little secondary education, he wasn't up to scratch in Egyptian." a true statement? Yes/no/unknown