Musk also claimed that "there have not been new car [brands] that have been successful for 100 years, apart from Tesla."
Some automotive brands that were founded in the last 100 years:
Chrysler (1924)
Volvo (1927)
BMW (1928)
Datsun/Nissan (1931/1933)
Fiat (1932)
Toyota (1936)
Volkswagen (1937)
Jeep (1943)
Land Rover (1948)
Honda (1963)
Don't forget his direct competition in China: electrical vehicle manufacturers BYD Auto (2003) and XPeng (2014). BYD outsells all of Tesla's worldwide sales and XPeng is an up-and-comer that will likely exceed Tesla's domestic sales by the end of 2024.
There's so many companies in China building cars, I don't know enough about that market to really speak to that. I tried to hit some big Chinese players with some history, though.
BYD and XPeng, however, are especially relevant because the former is kicking Tesla's ass in EV space and the latter is about to. (And BYD makes some kick-ass public buses too. Glorious vehicles!)
Chinese manufacturers are doing well in the European market too. It's a genuine worry for traditional manufacturers who have failed to innovate for too long.
Geely's another big one. They own Volvo but also produce cars under the Lynk and Co brand. Have good lease deals in the Benelux. Then there's Nanjing Automobile. Own MG and make a quite good (and very affordable) range of electric cars.
Honestly, I'm also sceptical, but if I buy a new car it's likely to be an MG 4 based on glowing reviews and affordability.