watchOS 3 Fitness app navigation

I like how the new fitness app has a list of workouts and when you tap on one it has a nice animation to workout's view controller which uses page based animation. I'm wondering how this is implemented or if its maybe using private APIs. The closest I can come is to modally present the workout's view controller which uses page based navigation. However, in the fitness app the workout view controller has a back button and doesn't look like it was presented modally. It appears to have been pushed onto the naviation stack. AFAIK, you're not allowed to push a page based presentation onto the navigation stack.