Actually it does meet the requirements. Pistol is defined in two separate sections, one defines it as an overall length of less than 16in. The second defines it as having a barrel length of 16in, so by that definition, it is legal. All other characteristics in the two definitions are the same.
Actually it doesn't. The definition you are referring to is for a pistol under the 'Oklahoma Firearms Act of 1971' which applies to Title 21 § 1289.1 through 1289.17 and not to 'Oklahoma Self-Defense Act' which applies to Title 21 § 1290.1 through 1290.25, which governs permitted carry.