Technically Zlatan's goal was more unique and difficult, something probably only he could manage with the incredible lift he had in the air and how he twisted his body in the air to angle his kick.
The distance to goal was much farther and the angle tighter so Zlatan's kick had to be more precise. Besides the fact both were overhead kicks they weren't very similar, Mexes was a chest down control followed by overhead kick, you see this type of goal attempted pretty often, but this one is especially nice because the ball traveled a good distance and had a nice curve. The chest down kind of overhead kick is much easier to hit than a direct overhead kick like Rooney's or Osvaldo's from last season. Mexes had time to turn around and place his body to strike towards goal after chesting it down while Boateng was screening two defenders so Mexes got time and space.
Zlatan's goal came from his vision of what Hart would do and understanding how he could take advantage of the situation and he also had to act quickly so the central defenders and Hart couldn't intercept the ball in time, to do that he had to kick the ball when it was high up in the air to get the right curve and power to the shot and he wasn't standing still but running away from goal when had to jump in the air which increases the difficulty.
And while everyone is entitled to their opinion I don't think scoring that goal in a Champions group stage game against Anderlecht would be nearly as important to Zlatan as scoring it in a friendly against England while inaugurating the new national arena and after years of the English public and pundits calling him talentless and a nobody, worse than Crouch and Andy Carroll. And he'd scored three more goals and won the game too.
For the team it was a special satisfaction that Zlatan scored the goal and had a man of the match performance opening the new national arena as Sweden's captain the same day a racists scandal broke in the news around a big political party who's previously declared they don't consider Zlatan to be a real Swede because he was brought up by immigrant parents.
The match was much more than a friendly.
