The Fortean Times forum has a very plausible explanation, with picture here:

Latest Reports Of UFO Sightings | Page 69 | The Forteana Forums

eburacum Papo-furado

My theory on this one has already been put forward, but here it is again; the 'jellyfish' UFO is a free-floating bunch of celebratory balloons.

If they say it is inauthentic, is that a NO?

Well, this isn't entirely true. Sure, the DoD hasn't said that it's real, but they did issue a sternly worded response stating that the DoD does not comment on classified content and they will be investigating leakers and prosecuting them to the fullest extent of the law.

The first thing you learn is that these government agencies never lie, so any time they don't answer the question when asked to deny something that almost certainly means it's true. It's the same reason why Lockheed Martin has repeatedly changed the topic when people ask them to deny they have the NHI craft in their possession.

I disagree that they never lie. And they also strategically don’t answer questions that they clearly could so as to minimize what can be inferred from non-answers.

But it does say something that the response is about leakers, not about fakery