The Jag's are the surprise team because in reality no one expects them to do that well this season.
Why does anyone even bother to form an opinion anyway, regardless if its for surprise team, Superbowl team, rookie of the year, MVP or whatever? Its human nature.
The reason the Texans are not considered a surprise team is because they did play the best teams tough, their now experienced and talented. The Jaguars are not built near that solid but they have alot of intangible players that may (may not) elavate their team to a better record than expected.