TFA talks about Google testing with "unknown IP", but doesn't mention any testing done by the author with cookies cleared or in incognito mode. This seems basic.
It is Google that needs "incognito" mode, not the author.
a search for "hvor ofte bør man dusje" in my english google, conencting from brazil shows havfruen4220.dk as 6th and 7th result, which is pretty high for a spam website
"hvordan regne prosent" shows 2 dk websites www.humanrebels.dk, and havfruen4220.dk as 9th and 10th results
could be since the OP clicked on these links to find out google made his personal algorithm show even more of this stuff
thus, I imagine a never ending cycle of even more spam could easily be generated, specially for an innocent user