Maybe we are in a Matrix, but I doubt it. That seems too complicated to exist. Can you find anything in writing from Musk that clarifies his belief about this? Musk studders so much he is hard to follow. Such a poor communicator a genius can be. He never had to TRY to communicate. People always had to suck it up and decipher him. He could never run for president. His interviews require English subtitles and commentaries.
Edit: I found this below from Musk. I don't understand how he makes the leap. Does anyone?
"He said he had discussed the concept so many times, that 'it's crazy'.
"Even if that rate of advancement drops by a thousand from what it is right now... okay, well, let's imagine it's 10,000 years in the future, which is nothing in the evolutionary scale. So given that we are clearly on a trajectory to have games that are indistinguishable from reality and those games could be played on any set-top box or on a PC or whatever, and there would probably be billions of such computers or set-top boxes, it would seem to follow that the odds that we're in base reality is one in billions."
Elon Musk Shares Strongest Argument We're Living In A Matrix Style Simulation (ladbible.com)