Keep reading.
“The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States; and nothing in this Constitution shall be so construed as to Prejudice any Claims of the United States, or of any particular State.”
To use Nevada as an example, the land in Nevada territory was land of the United States. When Nevada was granted statehood, only a portion of the land was designated to pass to the state, the rest was retained by the federal government. And if the land designated for transfer wasn’t available when it was finally surveyed, then that land didn’t pass. I think the Act can be found in 13 United States Statutes at Large (1864) starting at page 30.
Well, there’s nothing in the Constitution authority the feds to take such action and the presumption of the Constitution is US gov’t authority is expressly enumerated and delegated or it is not a valid act.
So here the default must be that land within a state belongs to that state, not to the feds because the Constitution authorizes no such federal ownership of land within a state except by the constitutional requirements cited.
The correct was to read and interpret the Constitution (as any law) is as written and originally understood and intended. The Resolution of 1780 http://www.minnesotalegalhistoryproject.org/assets/1780%20%20on%20Public is good material to help understand original intent here - except for Indian reservations, land within the state belongs to the state and the individual landowners.