Why did Dred Scott claim that he became a free man by entering the Louisiana Territory?

This question, of course, refers to the Supreme Court's infamous decision in Scott v. Sandford, the 1857 decision in which the Court, led by Roger Taney, denied the right of a black man to sue in a court, and denied the ability of the federal government to restrict the spread of slavery. Scott, an enslaved man who was carried into Wisconsin Territory by his owner, an Army officer, argued that being in Wisconsin made him free. This is because Wisconsin, as noted in the question, had been part of the Louisiana Territory, and in 1820, a political dispute over the admission of Missouri (also part of the Louisiana Territory) as a slave state. The compromise that resolved this dispute stipulated that all territories in the Louisiana Territory north of 36'30 north latitude would be free from slavery. Wisconsin, the territory where Scott had lived for a time, was in this area. So Scott argued that he was free, having lived in Wisconsin, and that he could not be reenslaved when he was taken back to Missouri.