Why the discrepancy?

You'll note that the cheaper listing doesn't show the bathrooms or kitchen and the photos they do provide are "virtually staged." Meanwhile the more expensive one was recently gut remodeled and has nicer views. That's likely enough to justify much of the difference, especially if one buyer got lucky and found someone who just had to have the apartment.

To augment nycseller's comment, in Stewart House there has always been a premium for the apartments with views of Grace Church (North) especially over those which face South into The Wanamaker Building @ 770 Broadway.

Also on a somewhat unrelated note there are 3 "flavors" of 2 BR units in Stewart House:
- Corner with balcony
- Corner without balcony
- "Flat"(facing only either all North or all South)

Within each of those 3 the layouts are close to identical or mirror image.