There are two conclusions that one can draw from this statement.
One is that Musk has a plan, developed from the very beginning of his career as a space entrepreneur. It is known that he is a Mars enthusiast and had thought about a privately developed robotic probe to Mars before settling on building a rocket company.
The other conclusion is that Musk has been reading too much of his adoring press and has succumbed to megalomania.
Oddly, the two conclusions may not be all that incompatible.
About 20 years ago, Robert Zubrin published a study of how humans to Mars expedition could be done on the cheap, called "Mars Direct." The mission would be conducted in two stages. The first would launch an Earth return vehicle and a fuel manufacturing plant, powered by a small nuclear reactor, to the Martian surface. Once fuel for a return journey is created from the atmosphere of Mars, a second ship would launch a hab module, a lander, and other equipment with a crew of four astronauts to land at the Earth return vehicle to spend 600 days on Mars before returning to Earth.
This scheme may be what Musk has in mind for a private Mars expedition. There are, however, two caveats.
The first is that the launch vehicle will have to be capable of tossing 40 metric tons and then 80 metric tons into a trans Mars trajectory. The Falcon Heavy that Musk will be testing next year will have considerably less capability. The envisioned Falcon X or Falcon XX might serve, however. Alternately, the smaller Falcon Heavy could be used to assemble and fuel a Mars ship in low Earth orbit before it is send on its way.
The second caveat is cost. Twenty years ago, Zubrin suggested that the cost of a Mars Direct mission would be $20 billion. However, done privately, without the complications of a government bureaucracy, Zubrin brought the price down to $5 billion to $7 billion.
Right now, Musk's SpaceX is having to rely on government subsidies to create space craft capable of taking people to and from low Earth orbit. A Mars expedition is by orders of magnitude more challenging. The cost of such an undertaking will be far beyond anything Musk alone will be able to manage. He would have to get private investors to chip in or else, more likely, rely on government funding to go to Mars.