When installing the NativeScript CLI, it will ask you to install or update the native SDK’s. However, given that you cannot get an iOS SDK on windows, since you are not able to install Xcode, they have provided you with an alternative option.
Instead of you having to use processing power and memory storage to compile and store the NativeScript project on your local computer, NativeScript provides their own cloud IDE (Playground). This IDE provides QR-codes which can be read from both Android and iOS devices in order to load the application directly onto the device.
However, I (as a non-mac owner) would personally suggest that the majority of development was kept on my local computer and only pushed to the playground IDE when I had to test something on an iOS device.