This is an example of someone being gracious and giving her the benefit of the doubt as to her meaning. Revere's goal was not to warn the British, but to warn the Americans. His famous ride had nothing to do with alerting the British, because that's fucking stupid. Why would you alert the enemy that you're ready to defend against his attack?
Revere got himself captured by the Brits and was held and questioned by them at gunpoint. And it was only then that he warned them they would be in grave danger if they attacked. During his capture, the British heard a gunshot and town bells ringing. They decided the town had been alerted to their presence, and called off the attack. This is in no way what Palin said. This is a matter of fuckin' record; of actual history, which you can read for yourself without taking my word for it.
These guys are simply allowing her benefit of the doubt for screwing up the details. But, imagine you're in an American History class, and you take a test on the subject. And that's the answer you give.
You think you're gonna get that question right when your test is graded? Or...since you're a teacher AMS...imagine if a student handed in a math test in which he said 2+2=5. You could give him credit for at least knowing that the two numbers do indeed add up to a greater amount. He had the basic idea at least in mind. But he still got the answer wrong.
This is exactly what these Professors are doing. Giving her the benefit of the doubt.
But to make matters worse, she had literally just taken a tour of the Revere House when she volunteered that bit of info. So, it would further be like taking an open-book test, or in the math test example, using a calculator, and still screwing up the answer.
The simple fact is, Revere rang no bells to warn the British, and the intent of his "midnight ride" was to warn the colonists (IN SECRET, no less), not the British. Which he only did under duress, at gunpoint, after he'd been captured.
Read your fuckin' history, folks. Don't take my word for it. And don't take some professor's word for it while he's busy getting his 15 minutes of fame. Use your own think-making-muscles.
"You must be proud, bold, pleasant, resolute,
And now and then stab, as occasion serves."
Edward II: Act 2 Scene 1, by Christopher Marlowe