Some material change their property to tempolary magnet if the temperature drop significant.
From the VDO look like the liquid nitrigen (I guess from the smoke and white freeze mark) freeze the bottom material and change their property to tempolary magnet. That why the top piece (magnet) float over. Then when you put it on the edge outside the liquid N2. The bottom piece warm up and lost their magnatic property. That why the top piece fall down.
Oh, I'm just guessing ;D ;D