In the begining of the manga/anime it was stated that the shinigami exterminated the qunicies. The only ones left were Uryu and his dad.
That's not true. Just because Ishida, Ryuken, (and you forgot Ishida's grandfather) were the only survivors
we (the viewers) knew of doesn't mean there couldn't have been others.
It makes little sense to make that assumption because first of all it isn't explicitly stated. And second, Ishida's grandfather was a
descendant of the Quincys. He wasn't a direct survivor of the genocide itself (obviously because he can't possible be that old). If he was a descendant then it means there were other survivors in their lineage. Likewise, it makes little sense to say Ishida's bloodline is the only surviving family. If they survived, then odds are there were others as well.
As for the rest of lubrication's reply, you're not getting the point. The point is that the Soul Society Arc and the Arrancar Arc have nothing to do with the current one. The SS and Arrancar arc were
bridged because Aizen was the mastermind behind
both of them. This final arc on the other hand has nothing to do with the events of the past two arcs. It's a fresh start with a new story. That's what he's saying.
Viewers will need little background to understand this new arc, and none of what they need to know lies in either the SS or Arrancar arc
