It's just because HTML markup uses angular brackets (< >), that's all :-)

https://docs.angularjs.org/misc/faq

Why is this project called "AngularJS"? Why is the namespace called "ng"?

Because HTML has Angular brackets and "ng" sounds like "Angular".

If I were to reach for a more specific answer:

Define Angular

"denoting physical properties or quantities measured with reference to or by means of an angle, especially those associated with rotation."

Might fit - you might assign an ng-property to a div or a span, but "most" html elements are not associated with rotation, hah

You could try to say a webpage / website has many angles and AngularJS is pretty much an all in 1 framework (MVC).

That's all I got though - don't read to much into it - it's just a name.