It would be wonderful if they planted that many trees and even better if they watered and maintained them afterwards. However, that requires close integration with the local communities and good governance. Those are more challenging than planting trees.
There was another article about how the original "pay people to plant trees" style green wall project already failed, and that a different, traditional way of protecting saplings from livestock was taking over successfully. Surprised it wasn't referenced here, though this article is about the climate effects if the project is successful, not about how the project was conducted.