If Elon musk was just a random schmuck posting on Twitter under a username and I managed to figure out his real name, address phone number job ect you could claim I was doxing even if everything I posted was public.
But he's one of the richest most powerful people on the planet and actively involved in politics while controlling one of the largest communications outlet in human history. This much power has to come with a much lower expectation of privacy so it would hardy qualify as doxing to say what city his jet is in.