But presumably average score for each group is used. I wouldn't think the difference in average score between the 200k group, and the 220k+ group would be great enough to cause that (and I don't think there'd be too many data points the farther you went out to have much influence on the average).

Unless they were using some type of weighted average for each interval and then skewed the $200k group by adding its weighted average in with the intervals beyond it, then averaging that. Which wouldn't surprise me given the appearance of the chart.