It is not really a misprint, but probably a term that is from an earlier version, where there were Stealth Talents which could be bought at several Ranks (like the Survival Talent “Tracker”, which you can take up to three Ranks in).
The Stealth Talent tree has a total of seven Talents. Each can be taken only once, so at Rank 1.
The “Living Shadow” Talent allows to add bonus d20s to your pool up to the number of total Ranks in Stealth Talents. That is due to each Talent being available only at Rank 1 a maximum of 7d20 if your character has all the seven Stealth Talents.
In other 2d20 games, the Stealth Talents come in several Ranks (like in Infinity, where the “Disguise” Talent has up to three Ranks).
As a guess, I would think that in earlier versions there might have been Stealth Talents with more than one Rank, but they were changed before the final version without changing the wording in this Talent.