Of course you can be wide open with someone behind you. Being in proper coverage requires both depth and position.This is not anywhere close to correct. A receiver cant be wide open on a deep ball when the defensive back is behind him.
While the safety was technically deeper than Jackson, Jackson had about 7 yards on him towards the middle of the field. If the QB threw the ball towards the other hash, it's an easy TD and he would be wide open. Instead, the throw was about essentially an arm punt on the boundary side of the wrong hash.