Latest theory: might have been an inflatable party decoration.
There was a morning radio station that did a silly stunt for a couple of years called the Vag Project spoilered link - mildly NSFW where they took a sex doll, tied her to a helium (weather?) balloon, along with a GPS tracker & a GoPro & set her free…until one year it went high into Class B airspace including near the glide path for a major airport (PHL) & a number of people (including myself) told them that’s a good way to take out an engine / potentially bring down a plane. Someone wised up & that was the last year they did that. It was funny while it lasted, though.
It (is) BALLOON!
I’ve quoted that for decades and never knew where it came from.