I see hooks land like this countless times. The hitbox is slightly larger than the hook itself.
If I were to explain this in simple terms from a coding perspective.... Let's say ANIMATION_1 is what the Thresh hook animation does when he misses a hook. Let's say ANIMATION_2 is what happens when Thresh lands a hook. What I see in that photo are ANIMATION_1 and ANIMATION_2 at the same time.
ANIMATION_2 is supposed to deactivate ANIMATION_1 when the hook lands so you don't get both animations playing at the same time. In this instance, there seems to be a slight delay on the deactivation of ANIMATION_1. The delay might be there due to the ANIMATION_1 animation playing all of the way out without being deactivated by ANIMATION_2 (Especially since it is a max range hook) quick enough. This is likely to happen every time a hook barely lands on the side of it's hitbox. There may not be a simple solution to this unless you made the hitbox the exact same size as the hook itself. Even then you might get a double hook in a frame or two where ANIMATION_1's hook is slightly longer than ANIMATION_2's. To stomp out the 2-hook problem, they would need to find a way to deactivate ANIMATION_1 before ANIMATION_2 even begins. However, I believe this is subtle enough where it should not be an issue in the slightest. The real debate should be about the size of the hitboxes and in my opinion, I think the current size of the hitbox should stay.
This is also the reason people might complain when it looks like the hook misses them, but then it suddenly switches directions and catches them. It is the same thing. 