Yes NPCs build like PCs can reach 20 in stats, this is why they are considered special NPCs. I've said that all long. Adventurers (PCs), Monsters, and Special NPCs can have stats of 20 or in the monsters case over 20. All others have stats from 3 and maxing at 18. That's what is says on pg 7.
Not that I'm disagreeing with the max 18 for most NPCs, but am I missing somewhere that it says 3 is a minimum?
I admit that was my assumption as well, I just can't find it anywhere. But I could be blind.