What do broad and narrow mean in the context?

What does broad and narrow mean in a general context suppose Broad traits are x, y, z and narrow traits are a, b, c, broad issues are f, g,h and narrow issues are k, j, h? If a trait suppose X cant be further divided and why do we call it broad?

In this context "broad" means generally applicable and with wide (lots of) applications. Examples for broad traits might be "being a good communicator", "being good with numbers", "being tolerant", "keeping situational awareness"

By contrast "narrow", here, means a very specific skill with limited applicability. Examples of narrow traits are "being an expert in the use of commas in 13th century Icelandic poetry", "being able to fix air intake valves on Ford cars made between 2003 and 2005", "being able to remember pi to 1000 digits"

[This is opinion, but you asked for the origin: The usage, i imagine, comes from the metaphor of shallow and deep learning. Imagine a pool of knowledge: shallow learning doesn't go deep into the pool but covers a broad area of the surface. Deep learning on the other hand, covers a very narrow area of the surface but goes deep into the pool.]

Edit answering you question in the comments:

If one were to believe in the type a/b personality theory one could say "There are two broad types of people: type-A people are outgoing and ambitious, and type-B people are introverted". The meaning of "Broad" here is "a rough approximation", or "a view from 1000 feet". Broad in the sense of "Broad brush strokes" made by an artist or a rough sketch.

The antonym of "Broad" in this sense is "Specific" not narrow, so I guess this would be an example you seek: It's not the divisibility that makes something broad, more that it's an approximation.