The link you provided referenced Tink Thompson and his "Six Seconds in Dallas" book. The theory proffered in that book was that the JFK kill shot = 2 bullets, fired from 2 different locations, striking the head of JFK at almost the same time. This would explain the multiple directions that material/matter was expelled + the head explosion.
Once again: Hargis said he saw no exit wound in the back of JFK's head. He saw no splash exiting JFK's head in the back. Only the side.
He was right behind JFK: if there was an exit wound caused by a second bullet why didn't he see it? And there is no exit wound seen in the Zapruder film. Or splash from the rear of the head. And there is no exit wound in the head shown in the autopsy x-rays and photos.
You can say that Hargis (somehow) missed it but if you do that then you open yourself up to questioning about what the other eyewitnesses said they saw re a exit wound. We all agree that eyewitness accounts are notoriously unreliable. Unless they're corroborated by other evidence we can't rely on them. In this case Hargis's account is corroborated - for me - by the other physical evidence.
The physical evidence is the problem for those that say there was a exit wound in the back of the head.