What's not assumed is that they had the same thought patterns. People don't derive ideas uniformly from the space of all possible ideas, they tend to think within the constraints and realities of past experiences. If you build a house, it's going to be similar to houses you've seen before. If you paint a painting, it's going to be a painting rather than some other means of expressing yourself with colored pigments.
In other words, ideas are subject to the same kinds of path dependence that technology is. When we see something that's severely anachronistic (outside of it's "normal" place in time), the initial priors are that things like the dating are wrong rather than ab initio invention of a whole suite of different ideas that just happened to be preserved for us.
Also, I wouldn't assume at all that knowledge would transfer outside of a localized area. It didn't happen like that in the so-called hearths of civilization like Babylon, Egypt, China, etc.
I don't think anyone claims that early humans were not as intelligent as we are now but the weakest link in the knowledge of how to effectively use levers or roll logs, or not (metaphorically) 'reinvent the wheel', would have been the eldest members in the community.
https://www.smithsonianmag.com/science-nature/in-roughly-150...
WRT "brain surgey" - the operation in question would be to relieve swelling under the skull that was pressing on the brain - probably caused by a blow.
The remaining skull would show that the hole was cut using an edge, likely extremely sharp flaked stone similar to a modern ceramic edge knife - an original blow would have splintered bone and caused a swelling, the splintering would have been cut away. Other evidence would likely have included signs that the bone restitched itself and "grew back" to a degree, demonstrating the person survived for some years afterwards.
I know nothing about this specific skull, there are others with similar work discussed in journals.