No. The article never said ‘butt’; it said ‘buttocks’.
A poster here on FR said ‘butt’ to kind of make the point “Well duh! Of course the butt (buttocks) are exposed it’s a “G-String!””.
You’re reasoning was poor despite your conclusion being plausible.
Here's the part you are missing; without the clarification of covering the anus; a jock strap would be acceptable beach wear. Obviously, this is not appropriate beach wear, yet a G-string is permitted. There is a reason why I chose the words I chose; you just weren't astute enough to understand the other ramifications.