Nope, depending on jurisdiction. In general, he can be sued for both torts, but the corporation can also be sued for the book. In practice, it will also be sued for the statement, which will be construed as an attempt to promote the book.
The general rule is that anyone may be held liable for their own tortious misconduct. It may be that other people can also be held liable, under a theory of vicarious liability. But the bad actor is still responsible.
There are exceptions. For instance, in California an employee of a corporation who commits a tort may not be liable individually for the tort if it was done in the course and scope of employment. There are also variations by jurisdiction - in some places in the world, the corporate veil is a shield over even the owners' tortious misconduct. So your mileage may vary.
Side note - it would not be unusual, in a situation like this, for Mr. X to be personally liable for the debts of Bad Books Inc., if it is a mere instrumentality of his own identity. In that circumstance, it would hardly matter who was made to answer because the damages come out of Mr. X's pocket. And, as a practical matter, a plaintiff will typically name both Mr. X and Bad Books Inc. if there is any basis for doing so, because Bad Books Inc. probably has insurance that may respond.