Windows server is exactly what they should have used.
Since you can customize and streamline the setup of Windows Server, that is precisely what they should have used for their control systems. The drones themselves likely are more advanced versions of any remote controlled aircraft but with layers of encryption. They probably also have considerably higher powered telemetry most likely operating in the near infrared frequency ranges. I doubt you are going to find those drivers on Windows Update ... lol
Speaking of the price, stop for a second and think about who we are talking about here; Ok, did that come to you? Yes, exactly they do not care about the price! After all, it is not their own money they are spending!