UWP vs Web development

I recently heard someone try and make this argument. (They were sucking up to Microsoft at the time.)

If I do web dev I have to learn at least 4 things, but for Windows, I can just learn UWP

Their thinking was that for web development they need to learn:

• HTML
• CSS
• Javascript
• Some framework (e.g. Angular)
• Possibly more...

They argued that they could just learn "UWP".
But I think that means several things too:

• XAML
• C# (or VB, or C++)
• An MVVM framework (MVVM Light, Caliburn.Micro, Prism, etc.)
• The UWP app model and platform-specific APIs
• possibly more...

I don't think this argument holds up.
The development of any piece of non-trivial software requires the use of multiple complementary technologies, skills, and techniques. If you ever think you can just learn one thing and then you'll be done, you're setting yourself up for disappointment and failure.

There's a similar thing I've heard from other developers and that's:

I don't need to learn Android (or iOS) I can just learn Xamarin.

That's equally flawed and in similar ways.