I don't see how you can draw any differences between the two. They're both cheating, so I don't see how you can justify one and make it seem somehow more palatable than the other. It was a dive, clearly, although I can see why players dive in those situations - in having to hurdle Carsley's desperate lunge (he was nowhere near the ball, which is worth remembering) N'Gog put himself at a disadvantage, his stride was broken making it extremely difficult to shoot or cut the ball back across goal, especially so close to the line.
He seems to touch the ball with the outside of his foot (though it's difficult to tell with that angle). Not really nowhere near it though.
No idea how the ref fell for that tbh, you could hardly make a dive anymore obvious.