The foot movement looks like an attempt at the character getting better footing for the action of shooting, and then moving back into a neutral standing position to reload. The reason it looks weird is people will tend to stay anchored on the "back" foot, and move the front foot, the opposite of what's happening in this animation. In my opinion, it might be best to keep both the character's feet planted, since people don't lean back to reload if they're planning to shoot more.