I think more than anything, mentioning that Jeb killed Vicki was intended for some sort of shock value to entice viewers back to watching since many people were either confused by or simply didn't like the storyline.
I never really got that particular plot development, because it doesn't make sense. In 1795/6/7 the Leviathans were recruiting Barnabas to join their cause. Just the two Gods, Haza and the other one, were alive, as far as we know. Jeb wasn't even in human form yet, he was still in the box. So, are we to believe that once Jeb reached adulthood in 1968 that he somehow traveled back through time, threw Vicki off Widow's Hill, then was thrown off Widow's Hill by Peter, and returned to the present, somehow excaping death while Peter was hanged for his murder? Pish posh.