But that's exactly the point, it actually directly contradicts the dossier, which points to Mueller conducting it's own investigation on the matter, and not using/relying on the dossier.
The only mention of the dossier or Steele in the entire report is a re-print of a Trump tweet (Page 111), and that Congress (not him) relied on that report to question Cohen (Page 139)
However, Mueller's report also points out why there was probable cause to investigate Carter Page: Russian intelligence officials had formed relationships with Page in 2008 and 2013