Could someone tell me why...

There wasn't enough light so it used a long shutter speed. So you got trails. I can tell a flash was also used that froze one of the many images. The shtter speed was too long.
This is a slow sync effect. Flash combined with a very slow shutter speed. The flash acts as a very fast shutter speed, freezing the action, but the shutter stays open continuing to expose the ambient light, and record camera shake.

On point-n-shoots this is called "night scene" or something like that.
Thanks for the fast reply. I think I am going to like this forum!

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