The statement is really true. There is an interesting and unusual story behind the most famous cemetery in the US.

After Virginia seceded from the Union in May 1861, Union troops crossed the Potomac River from the national capital and occupied the 200-acre Arlington Estate owned by the Lee family. Three years later the U.S. government seized this property. With Washington, D.C., teeming with dead soldiers and out of burial space, Quartermaster General Montgomery C. Meigs formally proposed Arlington as the location of a new military cemetery.

On the 13th of May, 1864, the first military man was buried at the cemetery. It was William Christman, a private from Pennsylvania, who died at the age of 21. Meigs directed graves to be placed as close to Lee's mansion as possible, and in 1866 he ordered the remains of 2,111 unknown Civil War soldiers killed on battlefields near Washington, D.C., to be placed inside a vault in the Lees’ rose garden. This way he wanted to ensure the house would never be inhabitable of the Lee family again.

Justice has been met in the end, but only ten years after Robert E. Lee's death in 1870. The Supreme Court held that Lee's estate was seized by the government illegally. It was ordered to return the house and the territory to the family in proper condition, which meant all the dead were to have been exhumed. Finally, everything happened another way: in 1883 Lee's son decided to sell the land to Congress, this way earning $150,000.

More Info: en.wikipedia.org