I think this illuminates the difference that makes the difference here.

A polymath is actually good at many things, not just has an opinion about them. This takes an unusual level of ability.

In other words a generalist is not a polymath, because the polymath is better at the generalised abilities.

That's what felt wrong about the article, it was conflating unusually talented polymaths with the ubiquitous averagely talented internet pundits :p