When displaying a box graph, pygal displays values outside of the normal zones. You can see the example on their site as well:
You'll notice that no values are above 16,000 or below -4000 (in fact none are below 0). It just doesn't display properly.
This is posted for anyone who doesn't look on the website for answers (which I don't usually).
There is a solution to this problem, and it is not resolved completely yet - but there is a quick fix. In the meantime, to make it work (as expected) instantiate the object like this:
box_plot = pygal.Box(mode='extremes')
You'll notice that the above example will be solved, and in fact to my knowledge this is the only way to make box plots work.
To follow the issue: Link to the issue request
