Just pretend somebody clever was working for Capcom at this time, OK, posters? I know it's far-fetched, considering most of us have also played RE1, but just... play along. I hate when some party pooper comes in and comes up with some judgement that nobody is that clever. I'll throw you a bone and say that yes, this is the same game that saved Leon by randomly having a pipe fall on the person who is aiming a gun at him.
Watching the scene, I can verify that it's not clear who lets go... for one thing, it kind of looks like Leon has her by the wrist. She wouldn't have to let go; he would. When he thinks, "what made her do that?" he's actually examining the body of Annette, not the gun. He does verify that the gun is empty.
Also, hey; keep in mind that Capcom didn't randomly retcon Ada back into the story. At the last battle, a woman with Ada's silhouette throws Leon a rocket launcher. This is more than enough to finally destroy the monster he was trapped with, saving him. Again, making us question whether or not Ada is completely or just mostly immoral.