So, it can't be a puddle with a reflection? As you noted it sure looks like there was water that ran across the sidewalk and then down the gutter:
And it seems like the sidewalk/gutter line runs through the edge of the blob:
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I'm thinking it looks like the edge of the blob goes from dry light-colored asphalt, to darker at the edge where the road is still wet and then the darker part that is actual standing water:
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Am I mistaken that the sun is coming from this direction looking at the shadows?
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Could there be a low spot on in the street where just enough water collected to create a dark spot or blob and then reflect the sun? And the reflection would appear to move across the surface of the puddle as the plane flew by, assuming it moves in the video or there is an actual video.
Or would the sun angle make the reflection in a different direction and therefore not able to be seen even if it was a puddle?