A rather mundane explanation if I may provide... Coca-Cola, in addition to its well known soda brand, also owns Fanta. It was probably just an employee who switched the bottles out during the bottling process. It's an internal operation either way.
I'm sorry, but when I read the title, I instantly thought "Looks like my summer vaccation is... over...." BUT IT'S JUST BARELY BEGUN! NU ROXAS, NUUUUUUUUUU! *0*