For a flagstone it's pretty straightforward. I'm not great with figuring out flagstones, but this one is not complicated. It's just big hexes and triangles.
It actually inspired a different flagstone pattern, which I've mapped out, but haven't folded yet.
If you're familiar with flagstones this will make sense to you. If not, there are many flagstone crease patterns which illustrate the underlying structure. They all share a similar architecture.
This photo of the rear shows the triangle twist triads that comprise the design that manifest on the front of the paper.
I'm pretty sure I did draw a crease pattern sketch. I think I left it at work. Will try to upload it at a later date.
Found the sketch. I didn't come up with the design. I just mapped it out so I could understand how to fold it. Now you can too!