Definitely a weird thing to highlight as a "surprise" but also not quite right, since it should be exactly half... and also that portion of the pie should be a semicircle (around 180 degrees even if it's 48%)... but it's significantly smaller than that somehow?

Net compensation includes bonuses and such. It's not just wages. The 48% figure is the cumulative total of people with net compensation < 30k. So it's not wrong by construction just oddly misleading.

If you look at the SSA data, It also highlights that the mean net compensation is about $48k. And 67.4% of wage earners have net comp below that figure. Which is in line with the graphic.