The choice of countries seems arbitrary. I thought the list was limited to EU nations, but Iceland and Norway are there. Then I thought it was EFTA countries, but Switzerland is missing. Then noted Belgium is also missing... I give up!
The article is based on recent Eurostat publications. Eurostat is no longer receiving data from the UK Office of National Statistics.
But as sibling comments noted, the whole article is a giant slop, confusing employee costs for employers (this is what the linked Eurostat chart is about) and net salaries.