There is a [video presentation of the paper](https://www.youtube.com/watch?v=-QjgvbvFoQA) which does a good job of explaining the inspiration for the study within the first few minutes.

It sounds like what they were intending to study is the actual variance that is introduced, on average, by imperfections in throws conducted by humans. Unless that's mistaken, it's a fair point to consider the n=48 here. Did they discover an average that can be generalized to humans or just to those 48?

Yes and what immediately jumps out to me as a source of bias is that they asked this small group of 48 coin flippers to flip thousands of times each. I would’ve thought it would be obvious that when you ask people to do something thousands of times they might do it in a different (and biased) way than someone doing that thing only once.

Get a hundred thousand people to flip a coin once each and then see what happens!