It's just page hits at D-watch.
I think the big 4 order of Linux OSs in actual use is probably still the same.
Debian
Ubuntu *counting all the flavors
Red Hat *RHEL & Fedora
Free BSD *Slackware
Goes down pretty fast after that, the rest being mostly derivatives of one or more of the above.
I could be wrong. Ubuntu may be #1 overall, but not even close on servers. That would Debian, with a number still actually growing.
TC