I think the clue in my last post is in the words "in Argentina".
Basically everything in Argentina with regards to the war is controversial. We still haven't admitted that two of their A4s flew over Invincible, bombing and strafing it as they went after it was hit by an Exocet.
As far as the footage goes, no idea how or where, just that "someone" saw it and Sharkey shot down an unarmed plane.