Depends on lens construction as well. Certain lenses use more blades to make up the aperture ring and you can see that in the number of arms in the stars.
I can't remember which lens I used but I have the 18-55 mm and the 50mm prime for the Canon T2i. I think it was the prime as I used it all night and don't remember switching, but this was a year ago.
If no added effect after the photo was taken, most likely that star effect was the result of smaller aperture with a small bright light source.
I shot under the aperture of f8, and I also shot at under low light since it was candlelight, with the ISO at 100 and the shutter speed around 30 seconds. However, I have not been able to get the same effect, even with small sources of light. I would also like to achieve this effect for video, at 1/50, so would the star filter work for that, or does it have to be a long exposure shot still? I could also stop it down to f16, as it was mentioned, but I think the camera may go into aperture diffraction at that point, or it just doesn't look as sharp as f8.