I've not been able to find the law this particular paragraph references, but you are aware that Wiki, and all other information relating to eminent domain, contain the same requirement? That the property to be taken is private property? What law or clause of the Constitution allows the federal government to seize state land, or allows states to seize federal land?
“What law or clause of the Constitution allows the federal government to seize state land, or allows states to seize federal land?”
There is no such provision in the real Constitution but who knows what may have been slipped into the synthetic Constitution, or the two million page Federal Register.
The procedure for how to reimburse the United States for property it claims to own when states secede is not well defined. It has only happened 11 times in our history.
The Confederacy recognized this and offered to negotiate all issues with the United States in an attempt to preserve the peace. With war potentially looming and thousands of lives at risk, Lincoln refused to meet with southern representatives.