And for the reasons he says so.

But what if the sun WERE from another galaxy? So what? There would be really no way of determining otherwise, by either dynamical or spectroscopic studies. Although stars in any one galaxy exhibit enormous variation in their properties, depending on the circumstances of their formation, history and evolution, the stellar differences BETWEEN galaxies are insignificant.

The nonsense Plait is debunking here is "yellow science", or "fake astronomy" as if real astronomy weren't bizarre and wonderful enough.

Why do these people do this? Its supermarket checkout line tabloid science; other than selling advertising space, it serves no useful purpose. And very often, it occasionally reveals that the authors of this rubbish often have enough knowledge of the field in order to make this stuff up convincingly. It kind of reminds me of those climatologists that work for oil companies and contribute to denialist websites and publications; they know better, but they lie anyway for the money.

The Wikipedia article on "Stellar Population", is an excellent introduction to this fascinating branch of galactic astronomy. I highly recommend it.