There's an interesting comment in that video that says the bird thinks it's an egg and it's trying to break it open.
I don't know if that's true but I wanted to point it out to hopefully get some answers here.
Initially sounds possible. Only question I'd have is...how adept is that kind of bird at slurping up splattered egg innards? That's a _lot_ of force it's using if it thinks it's an egg. If it's trying to eat it, wouldn't it either squish it in its beak or stab it a bit to just break the top?