Is the page that is left blank except for the notice it has been left so intentionally really blank?
This statement has been used in many printed materials to ensure the reader is aware there are pages that are supposed not to contain any content. Otherwise they might think there has been a mistake and they have received a copy with missing content e.g. due to a printing error.
The real question regarding the marked "empty" pages is should this concept be classified as oxymoron or paradox (or something else). The former usually is considered for sentences containing the contradiction, but here the sentence itself doesn't contain the contradicting part. But in spirit that feels like more appropriate designation.
From paradox' side there is a kind of paradox called dialetheia which is a statement that is both true and false at the same time. While not exactly a perfect fit either it also gets pretty close to the point.