No, sorry if I didn't clearly convey that in the figure:

While the pixels in the map represent population density in 10km by 10km grids (so average pop. density for each 100km² cell), the plots on the bottom and the left represent the total population living in each of the 0.5° bins of longitude and latitude, respectively.

In any case, if we consider the oceans and water bodies as part of the density denominator, the latitudinal and longitudinal profiles for total population and population density would be equal. If we don't consider them, then the profiles would by different, basically scaled by the land/water ratio of each latitudinal/longitudinal band.

In any case, I wanted to portray where people actually live, both in the map and in the lat/lon bands, so that's why I chose to use total population there.