I think they were "foolish" in some ways, but I think it is foolishness that is more like gullibility, a type of foolishness, than anything like stupidity. Old Major was a clever leader, and he had a vision that has impressed many people since the day of Karl Marx. The intelligent and manipulative pigs were able to take the animals desire for a better life, and convince them that it was possible if they could get rid of their oppressor (Jones), and form their own society. They were gullilble (foolish) when they believed that there could be a society without someone/animal in control. Blinded by the vision, they were unable to see what the pigs were doing, unable to filter facts from propaganda, unable to see that the rules were changing almost as they read them, and willing to work for a future that would never come to pass.
So their gullibility/foolishness certainly contributes to their opression. But this is not surprising ... it has happened in many societies over the years, and may be happening today.
I would say that it is very accurate. The animals don't see that they are being oppressed and therefor make it easy for Napoleon to take over. Boxer always says " Napoleon is always right". If Boxer had recognized that Napoleon was wrong he could have shwashed him flat.