Those same pages also list certain content (a scout rifle, a strike map, a crucible map, and a few armor sets) from 2015's The Taken King as exclusive to PlayStation platforms until fall 2017 as well. Taken King's marketing materials stated that the PS4's window of exclusivity would close in the fall of 2016, but Polygon reached out to Destiny publisher Activision and got confirmation that the extension is legitimate.
Activision gave no reason for the extension. Some of the confusion lies in Activision's no doubt carefully chosen wording: all exclusive content remains such until "at least" a certain period of time meaning Activision and Sony can hash out deals to extend it.
Not that that should keep Xbox owners from feeling put out. As Polygon notes, a one-year timetable has been established. Sony and Bungie entered into a timed exclusivity agreement before Destiny's release, the terms of which dictated that the PS4 version of Destiny would get content like weapons and crucible maps ahead of Xbox One and Xbox 360 editions.
For that precedent to be broken so abruptly, and with no heads-up from Activision, is understandably frustrating for many Destiny fans.