To further add to the idea that the concepts themselves were not foreign to people at the time, just read some classic scifi from Isaac Asimov or Ray Bradbury. Or even older than that, and check out some of Da Vinci's ideas. There are even ancient Greek writings clearly describing the idea of many modern inventions we take for granted today. People are rather imaginative and inventive, and can generally take a simple idea to extreme heights long before we have all the necessary knowledge and tooling to make it reality. Even now, we know how we might do a lot of stuff only seen in fiction like warp travel and Dyson spheres, nanotechnology, etc. We just haven't got some of the requirements to actually do those things nailed down yet.