Spanish cedar (Cedrela, often Cedrela odorata) is not a true cedar. It is a tropical hardwood in the mahogany family that the cigar trade adopted because it takes moisture, gives it back, and smells like the inside of a cigar box. Most wooden humidors and many empty boxes are lined or built with it.
The wood has to be seasoned in the box before it is asked to babysit cigars. Dry cedar will steal water from the leaf. See seasoning a humidor. It also adds its own aroma; that is a feature people like and a reason some collectors use other linings for long aging.
Empty branded boxes in the shop are often Spanish cedar. They are collectible wood, not a licensed tobacco product.