Read the information in the link over again. Slowly. It's a compact frame. It says the 49cm is EQUIVALENT TO A 56cm in their other frame styles.

From the site:
Frame weight: 3.1 lbs 49cm
Fork weight: .88 lbs (uncut)
Color: Paprika Red

Frame: True Temper S3 Tubeset
Fork: Alpha Q CS20 Full Carbon Fork w/ Carbon Steerer
Headset: Standard 1-1/8"
Bottom Bracket: 68mm; English Thread
Front Derailleur: 28.6mm; Clamp Style, Bottom Pull
Seatpost: 27.2mm
Seat Collar: 28.6mm Salsa Lip-Lock Included
Rear Wheel: 130mm Spacing
Sizes: 43, 45, 47, 49, 51, 53cm (49cm = Standard 56cm)
Color: Paprika Red
Tire Clearance: Fits up to a 700c x 25mm
Includes: Salsa Lip-Lock Seat Collar

Sizing Note: The Primero measures about 7cm
smaller than the Campeon. If you ride a 56cm
Campeon, you most likely ride a 49cm Primero.