This decision was about whether the whole "not being allowed on the ballot if you incite an insurrection" thing was intended to apply to the president, or just everyone else.

Obviously, by any rational reading of the English language. But law is about arguing over what things that seem obvious actually mean, and this was slapping down a lower court that was arguing that it did NOT mean what it obviously means.

“The decision reverses a ruling by a lower court judge who found Trump engaged in insurrection by inciting his supporters to violence, but concluded that, as president, Trump was not an "officer of the United States" who could be disqualified under the amendment. The Biden campaign declined to comment.”

From the Constitution, Article II Section 1:

The executive Power shall be vested in a President of the United States of America.

He shall hold his Office during the Term of four Years… :

… No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States.

In Case of the Removal of the President from Office, or of his Death, Resignation, or Inability to discharge the Powers and Duties of the said Office…

… Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:--"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States…

But sure. The person running the Executive Office of the President is not, in fact “an officer”…