The Article is not correct. N1 to N3 are all using the action from a grand piano. (see: Yamaha (US) Product Specifications)

So the N2 is not a upright Piano version - this is the NU1 ! (The "U" in NU1 standing for "upright" piano). See NU1 Product Specification:

"Combining the traditions of an acoustic instrument with the innovation of digital technology. Featuring the same acoustic piano action used in Upright pianos, and a refined, compact design."