The source files are exclusively Sketch, and Photoshop/PSD is absent. The UI design community has been shifting for more than a year, Apple started releasing UI templates in Sketch in addition to Photoshop in 2015 — Google even earlier.
Illustrator is still highly relevant for its strength, vector based work, while Sketch has surpassed Photoshop for UI.
The momentum is only increasing, even with bugs and issues found in Sketch. It's obvious the interface design community desires better tools. I wonder if Adobe Comet stands a chance with disruption we're seeing?