Yes, back then AI researchers thought that propositional logic was how human intelligence worked. Later, they abandoned this idea and instead turned to Baeysian probabilities as the most likely mechanism. Later they abandoned this idea and instead turned to connectionism as the most likely mechanism.

Suffice it to say that we didn't have a clue back then and we dont' have a clue now, either. We don't have any good model of human intelligence. We don't understand it. We can't reproduce it. We dont' know how.

And if you think that modern AI research is closer to that target because we now have good classifiers- well, think again. In the past, we had good inference engines. We had good ways to reason with uncertainty. All those things are useful, and they may even be components of intelligence, but they do not, on their own, constitute intelligence.

Clearly.