I'm not sure if there was never an official ICZN ruling on the matter, but Apatosaurus and Brontosaurus were synonymized by Riggs way back in 1903, so yeah, the former has been the proper name for over a century if that's what Mamba was referencing.
Berman and McIntosh first published on the likely partial skull of Apatosaurus in the Carnegie Museum collections in the late 1970s and the Wrongheaded Brontosaurus Saga came into public consciousness shortly after. Many people mistakenly assume this was the reason for renaming Brontosaurus, but it was well after the fact.