[privong]

That is not the same paper. The preprint you linked was published in the Astrophysical Journal Letters, and discusses a different quasar (SDSS J013127.34-032100.1, at a redshift of z=2.5). The Nature paper is about SDSS J010013.02+280225.8, at redshift z = 6.30. The author list is similar, so it is likely the same team. But the arxiv link is a different discovery.

[privong]

I made a typo: the linked paper in the parent comment to mine is about an object at redshift z=5.18, not z=2.5.