I'm wondering if the AT missile was fired remotely. I couldn't see anyone moving away from the firing location, and I wouldn't expect the shooters to hang around.
There was/is such a thing as 'horizontal-action mines' back in the 1980s, where the 'mine' is actually an AT launcher that is controlled by mechanism that senses the vibrations, sound and - possibly, now in 21st century - by IR signature.
In the video, it seems like there was infantry weapons' fire on the column, too.
(on an unrelated note, we have the "Threadmarks" option now here)