That's not true at all. The name was coined by Vonda McIntyre in the novel The Entropy Effect in 1981, and it only became canonical because novelist Peter David happened to be on set the day the Excelsior scene in ST VI was being filmed and he suggested it to the filmmakers. According to the novel's editor David Hartwell, interviewed in Voyages of the Imagination: The Star Trek Fiction Companion (p. 36), "Vonda corresponded with Gene Roddenberry and George Takei to give Sulu a first name, Hikaru. They both eventually agreed." They wouldn't have had to be talked into it if the name had come from them in the first place. Takei must have misremembered by the time of that convention.