I see the .22 as his back up as he reloads the 9.
I wouldn’t be surprised if the .22 has 2 rounds out of it.
Just my attempt to perform a bit of psychoanalysis...or profile. The Glock was the ideal choice for a primary and is not subject to malfunction. If he were worried about that, He would have carried a second .30 cal. or a larger bore weapon. The cost likely was not a factor either, because you can buy either a small bore .22 or a .30 or .38 for about the same money.
Just speculation, but I sense he had some grandiose ideas about enjoying the moment.
For some strange reason people look upon the .22 as if it is a toy. In a lot of instances the .22 has greater penetration than its larger siblings, due to its smaller cross section. True it doesn't have the knock down power, but it is a very effective killing round. especially if you can shoot it accurately.