My guess is that the second video might indeed be a balloon, or a series of them, filled with helium.
A theory:
I don't know if that is true but I would think that a balloon like that will expand the higher it flies up the atmosphere, because there is less pressure? If that is the case, it could explain the odd shape because parts of the balloon membrane are less thick then other parts, so that the balloon tends to expand on those parts that are thinner more, then those parts that are thicker?