No different than if he had been pontificating about man not walkng on the moon or Abe Lincoln not being shot in Ford's theater. Certain historical facts are not debatable issues unless you are a nut job. Not only do we have eye witnesses who saw the planes hit the towers, but there have been ample credible studies debunking all of these towers packed with explosives before the planes hit conspiracy theories. This guy doesn't deserve to be teaching anywhere.
If someone says they are an alien or their father was Yeti or any of the other crazy things people say chances are it doesn't get into mainstream media. But, whacko conspiracy theories do no matter how far fetched. Good thing MSM or as I like to say the PCP (Politically Correct Press) is not liberally biased or they would be presenting this as fact. /sarc