The 2D projection of a spherical shell isn't a uniform disc – it does indeed look more or less like a ring. (Consider the rough analogy of a swinging pendulum – it spends most of its time near the edges of its swing.)
From the page you linked: "Notice that the electron is most likely to be
found at one Bohr radius from the centre, in approximate agreement with the classical atomic model." That's approximately a spherical shell.
