Doesn't the following eShopContainers app break the MVVM pattern?

I was referring to a great PDF version of the enterprise patterns using Xamarin forms, but then I came across the following ViewModel which directly references the Xamarin forms namespace.(Line 12)

https://github.com/dotnet-architecture/eShopOnContainers/blob/dev/src/Mobile/eShopOnContainers/eShopOnContainers.Core/ViewModels/LoginViewModel.cs

The main reason it is used is for creating the command binding for the respective buttons. Is this supposed to be the right way of following the MVVM pattern? I thought Xamarin forms namespace should not be used in your ViewModels to avoid clean architecture.
Can you correct me if I am wrong? I always thought we have to create our own class that inherits from ICommand and provide its implementations of CanExecute and Execute.