When they were publishing pie charts and made you fill a little questionnaire every time you buy a bundle, the stats showed that Linux users always paid a little more than the average, and this exponentially added up causing Linux users to pay a much greater sum at the end of the bundle, in terms of total money spent.
I'm not sure I can find the charts now (they were live and per bundle), but I track Humble since day 1. I remember it well.
Some of the earlier Humble Bundles had Linux users contributing about ¼ of the funds but I don't think it was ever higher than that. [0] These early bundles were also before Steam for Linux was a thing so were a major source of new Linux ports (relative to the number of available native games).
I'm not sure I can find the charts now (they were live and per bundle), but I track Humble since day 1. I remember it well.