Same, I did an install with OpenSUSE Tumbleweed and the latest KDE desktop environment with all optional packages and goodies, and after a fresh boot into KDE with Konsole opened, the RAM consumption was from 580MB to under 760MB, similar to XFCE.
I don't know how the author got those huge numbers but I fell like something is off with his FreeBSD installation/configuration and is skewing the results.
I'd take those results with a huge boulder of salt.