i wonder if there is a certain technique to create such pictures? Thanks very much!
I've always just heard it referred to as Bokeh, though, technically that word has a much broader meaning than just at night, or those specific shapes that you can create. I suppose "night bokeh" might suffice.
This is, of course, speculation since I didn't shoot this image, but it looks like a night scene in a park, or some other public space, that has been massively decorated with Christmas lights. If the depth of field is very shallow, using a very wide aperture, most of the lights (if not all) would be out of focus and create that circle effect. I have a similar concept:
I took that in my bar at 85mm and f/1.8. The background is white Christmas lights, fairly close to the subject. Distance and size of the lights relative to the subject will determine how big they appear.
The correct term for what you are referring to is a "blur circle", which is what occurs to point highlights that are out of focus. The more out of focus a point highlight is, the larger the blur circle, up to the size of the entrance pupil (which is the ultimate limiting factor).
Bokeh, derived from the Japanese word Boke (ボケ, "haze" or "blur"), simply refers to blur...usually background, but foreground as well. Boke does not specifically pertain to out of focus highlights, which form blur circles. Blur circles are a specific aspect of photography, and when produced with a high quality lens that generates high quality blur, are usually quite pleasing.
In your photo, it does look like blur circles, however for a relatively small amount of blur. I also suspect they are produced by very small point sources of light...christmas lights, maybe the result of fireworks, etc.
It looks to me like the picture you linked to involves multiple mirrors. It seems to have been taken in some sort of studio with mirrored walls. I've attached a copy of the photo here with the exposure heavily modified. Looking at it, you can more clearly see what is going on.
I'm not sure what the light sources are (possibly well-concealed fireworks), but it seems that a mixture of slow shutter speed and imperfect focus made them into nicely shaped little blobs.
Hope this helps a little!