Sure, but how much time did he give them to respond? The CS people maybe need a few seconds to "load" first-order logic into memory and may have been thinking about it before he gave them time to put their hands up.

He could have instead asked:

"Raise your left hand if you can interpret this formula, and raise your right hand once you've determined that you wouldn't be able to do it without consulting a resource."

After a set timeout he'd have a better sense of where people stood.

That sounds complicated though. Maybe people just prefer simple consensus algorithms, even with imperfect results.