Here’s how I see it
A node is basically device or point within a network capable of creating, receiving, or transmitting data. So Anytype backup server is also technically a node (except it can’t create data like your devices).
I do see why it’s confusing, they are not calling it the cloud even though it is(?). Anton said this which sounds like they are not using the cloud even though they are using AWS:
Of course I welcome any correction.