The key part is that last paragraph. It means at least some of the dossier was independently corroborated.
Actually I believe several things about the dossier have been independently corroborated, but many of those things were not really related to any of the juicier headline-grabbing details. Just technical stuff, so-and-so Russian person was a agent for such-and-such Russian intelligence service, etc. Nevertheless, so far, the dossier has proven right whenever enough evidence was available to prove or disprove it… which still hasn’t been a lot, yet.