You're right based on the modern day thinking of what the periodic table is but you're wrong to suggest that people knew what they were doing from the very star

You're right based on the modern day thinking of what the periodic table is but you're wrong to suggest that people knew what they were doing from the very start. The formulation of the periodic table is quite like modern day data science. Chemists even before Mendeleev observed patterns and tried to build a model to predict missing ones. The beauty is that this was done without understanding the underlying mechanism of how it all worked, ie what makes an element (protons), what makes their periodicity (electrons). That came 50+ years later when we discovered protons and electron orbitals. So going back to the article, their approach is fine because they're just formulating some model from observed patterns. Their reasoning for the underlying mechanism could be completely wrong but that's fine too until a better model comes along.