MTG Salvation

I just got a second booster box of Modern Horizons and one of the cards is Nimble Mongoose. I read the card and it makes no sense to me. It has shroud, but it also has an ability that states "Nimble Mongoose gets +2/+2 as long as seven or more cards are in your graveyard." This would make sense to me if it was hexproof, but because shroud prevents any spells or abilities targeting the creature, I don't get how it's ability can affect it. I'm not specifically choosing to target the creature, but NM's ability clearly states it only affects NM, meaning it's targeting it. Can someone explain this to me?