[duchenne]

Yes, there is a possibility that the sample is biased. But that does not matter for this experiment.

The OP says that the model should be built with people in the same room than him, and then the human RNG should be executed with the same people.

As a consequence, OP has to capture the bias of the people in his room to make his RNG work.

The model would break only if the people in the sample change their strategy to pick random numbers after some time.

The data from Reddit is just used as an example of how to make a human RNG from redditer random picks.

As long as the training and testing are done from the same group of people, there is no issue, even if this group is biased.

Moreover, I don't see any prior reason to believe that redditors and HN readers would have different biases. That would be an interesting experiment, though. However, the predominance of the number 7 in article's data might be a western culture thing.