I really don’t believe they directly create a shape out of the flowlines. And flowlines are no CFD, but a CFD Analysis can output flowlines. You can create this also differently. In the old forum, there is also a very similar effect created, based on a particle tracing a path of minimal curvature change on a curved surface using Runge-Kutta integration. This is really just a visual effect than a meaningful analysis. I cannot find the link anymore, I was translating David Ruttens VB script into C# there…
They often just create these flowlines and then they model a shape based on that. Sometimes they pretend to do things like this auto-generated, but as I said, it is often not quite true. Furthermore, even if it is from a CFD simulation, there is no validation that the simulation is correct.
I propose to just model a shape like this manually using sub-d and then just fake anything else.
There is also plugin called FLOW, but you can also use the default magnetic field lines.