Fish "coming back to life" after being frozen
I have no idea what's the real reason for the survival of the poor fish, but I would guess this is all in the timing. I know for certain ;-) that one can submerge a hand in liquid nitrogen for a short time or in general one can pour liquid nitrogen on the skin with no harm done whatsoever.

The reason is that the difference in temperature that interface (-180 deg C or so for liquid nitrogen and 20-30 for the skin surface) is so large that nitrogen vaporizes instantly and does not penetrate/affect the tissue. The demonstrator could have pulled the fish with bare hands.

I think that for the goldfish the time was too short and while it was cooled/shocked a bit, it might have been too short to do any serious damage. But -

As a scientist, I can't help but notice that we don't really know the condition of the fish before or after the liquid nitrogen 'treatment'. We only see it flapping for a few seconds when back in water. I wonder what happened to the eyes and the mouth, both quite sensitive tissues for such a shock. Also, the water the fish was in was a factor probably, providing additional buffer between the fish and the liquid nitrogen.

Last but not least, the ethical committee quite certainly did not approve that demonstration.