Wow. That's pretty impressive
Not to say they couldn't have shipped it in less time. Of course they could have. But it sounds like they shipped something very well built.
Development on Android tends to be slow overall, owing to numerous intricacies of the platform, but I believe that in general taking some extra time to roll out a clean and polished version 1.0 will pay off when it comes to 2.0 and 3.0. It's always easy to move fast in the beginning, use lots of duct tape and snap something out rapidly, but it comes at a cost and then you get bogged down further down the line
Right now we are working on a rearchitecture and are finding that creating dynamic views in the Activity/View requires business rules we are putting in Presenter. But the Presenter doesn't have context.
On Android MVVM is more difficult than MVP in my opinion (the most popular choice, not counting spaghetti projects), mostly because the platform doesn't provide the "glue" needed to bind viewmodels to the UI layer. At first glance it looks like they did it without overengineering, which is another trap as far as these matters go.
Clearly a work of very good experts