This is noted in another comment, but it should be a top level comment... Magnus actively has COVID and has said that it was affecting his energy levels and ability to calculate during the early rounds of the tournament (during which this game happened).

And Pragg wasn't even the lowest rated player to beat Magnus this tournament! Eric Hansen, aka popular chess streamer "chessbrah", is even lower rated and also beat Magnus, which again you would not expect if Magnus were playing his usual level.

So still a great win and great accomplishment for Pragg, but a little context would have been nice in the article.