It's only lying if he doesn't believe it. And he demonstrably does. He has a whole division at Tesla designing a humanoid robot for mass production in the next few years on the assumption that the AI will be ready by then. He keeps removing sensors from their cars on the assumption that AI can replace them in a few months' time. If he didn't believe his own statements about AI he wouldn't be doing those things. It may be borderline delusional, but that's not the same thing as lying.

Consider that in the past plenty of other people in the industry have underestimated things that he's overestimated, such as the potential for reusable rockets and the timeline for electric cars becoming viable. And those have been incredible success stories for him, despite his initial overestimation, which really was overestimation, that many called stupid at the time. And AI may yet turn out that way too. Even if he's wildly optimistic about timelines, he may still end up closer to correct than the conservative establishment in the industry which would prefer to see the status quo go on forever, like with disposable rockets and internal combustion engines.