This is about 3rd party trackers masquerading as the 1st party by asking the hosting page to provide a CNAME under their own domain. With the tracker hosted under the 1st party's domain, they work around people that deny 3rd party cookies.
The example at the top of the thread: https://www.liberation.fr/ has a tracker from f7ds.liberation.fr, which is really part of tracking provider Eulerian.
f7ds.liberation.fr. 3599 IN CNAME liberation.eulerian.net.
TL;DR - the entire point of this is to let 3rd parties continue to correlate your identity by hiding as part of the 1st party.
The example at the top of the thread: https://www.liberation.fr/ has a tracker from f7ds.liberation.fr, which is really part of tracking provider Eulerian.
TL;DR - the entire point of this is to let 3rd parties continue to correlate your identity by hiding as part of the 1st party.