It is leveling of pay throughout the career for CS compared to growth in the first 8-10 years for engineering followed by general leveling, at least from what I see. Entry level engineers see salaries increase 10-15% annually at first! and then leveling off around $110k to a 2-3% annual increase. (There appears to be an age biased decrease after age 55 or so for the median changing jobs as well.)
This happens in cycles... Bubbles if you will. It isn't really sustainable, and it distorts the market. The numbers don't make much sense without a lot of detail.
For a given aptitude, earnings potential in engineering and CS are similar.