What is Shalvus Martholio’s passive Perception?

I’m fairly new to D&D, therefore I’d like to verify this to make sure I’m perhaps not overseeing some rule I’m not aware of. I’m not trying to be pedantic 🙂

Shalvus Martholio, from Storm King’s Thunder Appendix A (made available by WotC in the link below) has a Wisdom of 14 (+2). Based on the skills bonuses, I derive that he has a proficiency bonus of +2. The mentioned skill bonus for Perception is +4 (makes sense +2 and +2). Yet, his passive Perception is only 12. Shouldn’t this have been 14 by adding: 10 (base) +4 (perception bonus)?

Storm King’s Thunder, Appendix D: https://media.wizards.com/2016/dnd/downloads/SKT_AppD.pdf