Right, but that doesn't really explain anything. Maybe the author is concerned about some future changes in the nginx project and they're preemptively moving aw

Right, but that doesn't really explain anything. Maybe the author is concerned about some future changes in the nginx project and they're preemptively moving away from NGINX, but even if that's the reason, it's not much of one. If they're using the open source version of NGINX, then it seems highly unlikely anything will change that will impact them.