I'm also leaning in the bug direction, although the dandelion idea isn't half bad either. However, if it was not a windy day, it seems less likely that a dandelion seed would be up that high. At first, it seems like it's far away, but without knowing its actual size, it's just as likely to be close.
I also agree with ms coast that it's impressive you even saw that thing. It took a few tries, but I did eventually get it stopped on the screen. Cannot tell what shape it is, but it's definitely something there for the briefest of moments. Just curious, do you watch all your videos at 1/4 speed or were you able to see this at regular speed? Kind of makes me want to go back and slow some of mine down.
You said you got it a 2nd time on the return trip? Was it going the same speed? If so, that would tend to lend credence to the dandelion seed.