Gravenhollow is not suffused by faerzress but by a magic that is powered by faerzress.
Reading through the chapter on Gravenhollow, I could not find any information on if Gravenhollow was suffused by faerzress. Since that it is not actually stated any where, I tried to find if there were similarities in the magical effects in Gravenhollow and those caused by faerzress.
One of the effects of faerzress is:
Areas suffused with faerzress are always filled with dim light.
This seems to clash with the description of Gravenhollow which states that:
The oppressive gloom of the Underdark is replaced by light and a sense of openness that brings back memories of the surface world.
Gravenhollow also states that:
Though divination magic works normally within the library, no divination effect used outside the library can discern any creature, object, or location within it.
If Gravenhollow was faerzress-suffused then any magic would not "work normally" and instead be subjected to the Wild Magic Surge table on a roll of 1 on a d20.
None of the effects of Gravenhollow seem to align with the effects of faerzress-suffused areas. Combined with the fact that Gravenhollow is not explicitly stated to be suffused by faerzress leads me to believe that it is not suffused by faerzress, but is affected by a different magic.
Using your quote, I would think that the faerzress is instead used to power another kind of magic.
Gravenhollow was carved from a titanic geode whose crystals are imbued with magic that concentrates faerzress. The magic that suffuses the library profoundly affects time and space, altering the perceptions and reality of all beings within its walls.
Since that the quote says the magic that suffuses the library, rather than the faerzress that suffuses the library, it indicates that the magic is not faerzress.