It's really not that hard to believe.
When this team switched from Vince Young to Kerry Collins, it was an unexpected change and no team was prepared for it. Add to that, Chris Johnson caught the league by surprise. While everyone ridiculed the Titans for the pick, all he did was perform at an extremely high level.
The team proceeded to go 9-0 with Collins, against what turned out to be a pretty mediocre schedule. Couple tough games mixed in with some struggling teams. I won't give Collins credit for the first win because he entered that game with a lead.
Titans finished the season 3-3, 3-4 counting the playoffs.
If you watched this team during the course of the season, teams were starting to figure out how to pressure this team pretty well, and it carried on to this season.
The loss of Haynesworth and Shwartz only compounded the problem. Teams knew that the defense wouldn't be as strong, and the knew they could hurt this offense by forcing Collins to win these games, which he can't. The failure of Collins at the QB position is forcing a weaker defense to constantly stay out on the field.
The result? This team doesn't stand a chance.
Said pretty much the same thing back in April:
http://www.sofantasyfootball.com/nfl/f2/vince-young-says-hell-shut-up-2009-a-27007/#post294138