Yes, just a joke. He can’t really think that he belongs there. At least, not while he’s alive. After all, even Teddy Roosevelt, the youngest and most Republican member of the enshrined quartet was dead many years before his image shone down from the mountainside.

As for the company he would be keeping, Trump is neither the warrior as Washington or Roosevelt, nor the statesman or diplomat of Jefferson or Lincoln. All four fought for what they believed in, knowing that it could result in their deaths. These four presidents were picked because they commemorate the founding, growth, preservation, and development of the United States.
Washington set the precedent of limited terms in office because he didn’t want our new country to be subject to a king in everything but name.
Jefferson doubled the size of the young country.
Lincoln did his best to keep the country intact as one country, not two.
Roosevelt stood up to corruption and provided that the wonders that made our country special would be left intact for future generations to enjoy.

Trump treats politics like his companies. He expects absolute rule and absolute obedience. He preferred deferments to service to his country. His empire grows on the backs of contractors he does not pay and people he bullies. But that didn’t stop companies affiliated with his name from failing. His god is the almighty dollar, and based on this treatment people without enough dollars don’t deserve to be considered. If Trump finishes this term of office, and goes on to a second, the United States of America will undoubtedly have fewer states when he finally leaves office. Trump’s best advisors have been steeped in corruptions of their own, and in the name of the almighty dollar Trump is guaranteeing that the most beautiful and fragile parts of our counry will be sold to and despoiled by corporate greed.

So, yes, by all means, Trump must be joking about being on Mount Rushmore.