Well, that depends on how you measure if they're the same. Obviously they are not the same spot on the body, if that is all you're looking for then of course they're not the same.
But a strike that hits the very center of your belt line is still able to move your cup which leads to discomfort at best and can be straight up painful at times.
If fighters fought without a groin guard, the only illegal area would obviously be the groin. But they do wear a groin guard, and since that groin guard needs to cover the groin and isn't custom fit (at least I haven't heard of custom cups) it will be quite a bit larger than the literal groin.
Any strikes that hit within that larger region will cause groin pain due to the cup being shifted. But since you don't want fighters rolling on the floor in agony of their testicular pain, all strikes that hit the cup should be illegal. Otherwise that could be targeted specifically, which would essentially be just as bad as unprotected groin strikes in the first place.