Yes, that's the only information the plugin produces.
The idea is that you can "reverse engineer" existing pieces of art and see what colours were used in them. What colours to choose for your art (be it painting, digital art, photo, movie etc) is an important decision to make – you don't always want to use the full range of colours available, but rather limit your palette to achieve harmonic results or specific moods.
I'm currently reading "Color and Light" by James Gurney, who describes limited palettes and gives examples by placing geometrical masks called gamut masks on a colour wheel.
He's also made a couple of blog posts about it. That's what inspired me to make this plugin so that I can inspect the colour wheel distribution of various things.
Of course, it doesn't really help you if you want to paint something from scratch, for that, you need to have something that limits your palette. MyPaint lets you set gamut masks on the colour wheel, and it has an export to GIMP palette option, but I paint in MyPaint anyway, so I haven't tried the export.
For example, to paint something like my example above with the yellow trees, I could use a mask like this:
Quite interesting that a random snaphot I took turns out to have almost a perfect triangular gamut mask like right out of a textbook.
Your expample, too, has a very limited palette that's almost triangular.