If you are an EU citizen (or a citizen of one of the other Schengen Area countries) then yes, you have freedom of movement and can live and work anywhere in the area without a visa.

But the article isn't talking about being an EU Citizen. It's talking about having to count how many days have been spent in the Schengen Area by a third-country national.

Citizens of certain other countries (e.g. the USA or UK) can enter the Schengen Area visa-free for tourism or limited work-related activities (for up to 90 days in a 180 day period), but are not allowed to just do whatever work they want to.

Note that the comment I replied to was talking about non-EU Citizens.