Are your eyes better than mine?
It's based on the tetrahedral kite, a tried and tested design. In my experience, kites like this have amazing stability and huge amounts of lift. This thing should have needed a serious effort to restrain.
But it only gets a few feet off the ground, and then only just.
The huge banner will have something to do with it, but not a lot.
I've squinted at the video of it in flight, and I may be imagining it, but are a lot of the triangular cells the wrong way round, contributing no lift at all, just a lot of drag?
Can you have a look, and see if you can work it out?