My understanding is that an “unskilled” job has always meant a job that doesn’t require previous experience. It has nothing to do with how hard the job is or how valuable the work is, just whether or not it requires prior training or not.
One example from the article was working as a caregiver. My brother worked as a disability carer while he was training to become an engineer. I was living with him at the time, and he started out with a baseline ability to care for others, no particular skills that an average person wouldn't have, and no qualifications other than a police check and a first aid certificate. He was essentially paid to drive people with mental disabilities around and not get frustrated with them.
On the one hand, I get why someone with 20 years experience as a disability carer wouldn't want their job to be seen as something a uni student can pick up in a week. On the other hand, my brother could just go become a carer, so it's not entirely wrong.
My impression is a pervasive disconnect (again, at least in the US) has started to develop between those types of mandatory credentials and the actual skills required for the jobs, or even for training for the jobs. So say, the credential starts to be equated with the skill in hiring or for training admission, when it only bears some weak relationship in reality.
There's lots of causes of this I think, but the net result is a spurious decrease in competition, increased prices, and greater income inequality and underemployment. I think the article is a little odd but is pointing to these kinds of issues.