That's a fair statement. The Colts have allowed more pass completions, but for less yardage, as opposed to an opposite team, the Saints, who have allowed only 58.1% of passes to be completed but have an 11.8 YPC rate.
Last year, there were about 515 pass attempts on the average team. A team with a 66.1% completion rate with 10.1 yards per catch with 515 pass attempts - the Colts - has allowed 3178 passing yards, or 199 yards per game. A team with a 58.1% completion rate with 11.8 yards per with 515 pass attempts - the Saints - has allowed 3531 passing yards, or 221 yards per game. Of course, you don't need me to tell you that the Saints pass defense is terrible.
Following this same projection system, it is clear that the Colts passing defense has improved. The Colts of last year had 10.6 YPC and a 65.4% percentage passing rate, giving them a projected 3570 passing yards and 223 yards per game - even worse than the Saints this year. This improvement could be due to the play of Bob Sanders, the acquisition of Marlin Jackson, the play of Cato June and other linebackers, the pass rush of the Colts defensive line, or, more likely, a combination of all of these circumstances.