The 10th ranking is for "metropolitan areas" compared to other metropolitan areas and the 51st ranking is for the City of Shreveport compared to other cities. I'm not quite sure how a city that ranks 51st gets combined with a city that even safer to move up into the top 10, and their explanation of their methodology doesn't indicate how that could happen.
http://www.morganquitno.com/methodology07.htm#Method