To be fair it did look like they only missed by a few yards, which if you where firing on frigate or a destroyer would likely still be a hit.

Plus presumably there is some sort of radar based gun director and it’s not going to be much use detecting a small fibreglass boat.

The gun, for direct fire, will take direction from the forward 909 radar or from a manned optical director called the Local Area Sight or LAS. Collimation errors between the LAS and the mount can give you a couple of yards deviation and usually, as described, this is inconsequential as the things you try and hit with the main gun are bigger that a few yards across!.