If that's how he scored, then Heritage's ratings are flawed. I can cite numerous issues where Paul's position is NOT conservative.
The Heritage Foundation
Founded in 1973, The Heritage Foundation is a research and educational institution—a think tank—whose mission is to formulate and promote conservative public policies based on the principles of free enterprise, limited government, individual freedom, traditional American values, and a strong national defense.
We believe the principles and ideas of the American Founding are worth conserving and renewing. As policy entrepreneurs, we believe the most effective solutions are consistent with those ideas and principles. Our vision is to build an America where freedom, opportunity, prosperity, and civil society flourish.
Please recall that Hertiage is run by the very conservative Jim Demint
From Wiki
Jim DeMint is a member of the Republican Party and is aligned with the Tea Party movement. In 2011, DeMint was identified by Salon as one of the most conservative members of the Senate. He founded the Senate Conservatives Fund, a political action committee (PAC), which supports conservative, small government, Tea Party–allied Republican politicians in primary challenges and general elections. In 2013, the PAC endorsed a strategy to defund the Affordable Care Act that culminated in the 2013 shutdown of the federal government.