This is what I saw:
Remember the KJ turret has a 180-degree view, it can't lock on to players behind it.
The first jiggle out activates the turret and it shoots one bullet.
He jiggles back behind the door of the wall and the turret locks back to default and shoots its second shot.
He jiggles back out even wider and the turret shoots its 3rd shot heaven as he is behind the turret's 180 view as he swung so wide so the turret goes back to default and shoots heaven.
You're asking why it didn't target him when he was 'in the open' it's because he was behind the turret's 180-degree view.
This has been a feature for so long, I don't think FPX's win should be taken away because of this.