Update

NFL has said Pete Morelli was in error.

We got the definition of "catch" I've been looking for. Quoth Mike Pereira:

"The definition of a catch -- or in this case an interception -- states that in the process of making a catch a player must maintain possession of the ball after he contacts the ground," Pereira said.

"The rule regarding the performing of an act common to the game applies when there is contact with a defensive player and the ball comes loose, which did not happen here."