They applied smoothing/Sub-division to the mesh - that’s why it’s also smoothly curved overall, despite having only a few polygons.
To add to what Richard has said.
When you click on the smoothing under properties it doesn’t actually change the way the mesh looks until you click on the lightning bolt under Dynamic Geometry. It allows you to view what happens with smoothing applied and to also have fewer polys to manipulate.
If you click on the the lightning bolt it will then display all the polys in the viewport but the poly count at the top changes as soon as you apply the smoothing but will change back if you click on the lower boxes.