[oersted]

Indeed. I'd say that the issue is that they are misinterpreting the word "collecting". The principle is true if you are collecting or observing data live, but this data was collected long ago and with a much wider scope: when the games were recorded.

What they are doing here is sampling the data after the fact, and obviously one needs to take a uniformly random sample of a dataset for any statistical analysis done on it to be representative.