Great observation! Andrew waived to the camera, not to the girl leaving.
The news descriptions have all been variations of "waving a cheerful goodbye to a young woman" (washington post), "waving goodbye to an unidentified woman" (npr), "waving goodbye to a young woman" (cbs), "he bids a cheerful farewell to a young woman leaving" (thetimes.co.uk), "waving goodbye to a woman" (The Guardian), "waving a woman goodbye" (The Independent), etc.
I think I read the description before I saw the video, and it influenced what I thought I saw.
It looked like he may have known (even fondly)
the person taking the video at the time.
Maybe now not so much....
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