Houston is well below a number of cities that have strict gun laws. D.C. being the most glaring example; among the strictest gun laws in the country, and the highest crime rates.

Houston also has a significant low-income population, and experienced white flight to the suburbs on a massive scale through the 70s and 80s; leaving behind a wrecked shell of a city (downtown has only recently started to come back to life; when I lived in Houston, downtown real estate was dirt cheap, but everyone was afraid to go there after dark).

In short, I don't think it's anywhere near as simple as "guns lead to more/less crime".