Technically true. Although wasn't Gone with the Wind playing in theatres for way longer than any movie today would?
Estimates for Gone with the Wind's adjusted gross have varied substantially: its owner, Turner Entertainment, estimated its adjusted earnings at $3.3 billion in 2007, a few years earlier than the Guinness estimate; other estimates fall either side of this amount, with one putting its gross just under $3 billion in 2010, while another provided an alternative figure of $3.8 billion in 2006.
Which film is Gone with the Wind's nearest rival depends on the set of figures used: Guinness had Avatar in second place with $3 billion, while other estimates saw Titanic in the runner-up spot with first-run worldwide earnings of almost $2.9 billion at 2010 prices.