Pet peeve. To the author. The professor was not hoisted on his own petard. A petard is not a flagpole or ship's mast. A petard is a small bomb. The professor was hoist by his own petard.
Petard hoisting is not even appropriate here, since he did not “fall into his own trap” (another meaning of the term) since he was not setting a trap - But he was certainly caught lying over and over again...
More closely resembles the phrase “Methinks the lady doth protest too much”