Not inherently, perhaps, but humans are believed to have begun ’’behavioral modernity about 160,000–70,000 years ago,[27] and possibly earlier.[28]
That is, in the period you’re imagining, humans were not only the same species we are, but they were developing language, technology, culture, etc.
And again, even insects know about reproduction. So do animals. They may not know the exact cause and effect and details we’ve learned, but “discovering reproduction” happened before humans became human. And we get reminded every time a woman gives birth.
Once people have language, it doesn’t take long for them to start talking about it, and making observations and deductions, not only about humans, but about the other animals as well.
People in the past were as smart as the smart people we have now.
The only people who are confused about reproduction, are children and others who are misled or have information withheld from them for cultural or religious reasons.