Can you provide a different source on that? The govcloud page you've linked says operated by US citizens, not built by US citizens. I'd be pretty surprised if they did the latter. Standard practice as I understand it is to simply run the standard software in a separate environment. A recent Propublica report [0] pointed out that Microsoft was hiring citizens to escort the actual engineers that aren't citizens, for example.

[0] https://www.propublica.org/article/microsoft-digital-escorts...