I looked at map of the area, and a half mile is about right.

There is a ridge that can been seen from our kitchen window. On top of that ridge is a bench for weary hikers. It's a standard size park bench, dark brown, with the back rest measuring about two feet wide and five feet long. According to my GPS, that bench is 0.71 miles (horizontal distance) from our house. Using standard 7 x 35 binoculars, I can clearly see this bench from the kitchen window, I can see people sitting on it. If they were holding up a large plastic garbage bag, I could see that as well. At a half a mile, I can clearly discern a 4 inch by 4 inch fence post. When I'm in the field, I use binoculars all the time to pre-map adjacent areas and am used to looking for subtle clues to the geology from thousands of feet away.

When the bag floated over my head, it was no more than a hundred feet off the ground. Pretty obvious at that distance. I could see the seams. Total elapsed observation time: about five minutes.

Now had you seen this floating bag, I can only imagine the conclusions you'd have drawn!