Without knowing all the facts it's hard to give a definitive answer but the following might be of interest.
My user name derives from the first CAA prosecution I defended. Night mail flight commenced an approach with the reported RVR below minimum. Another flight landed a few minutes before also having commenced his approach with RVR below minimum. First aircraft called visual and on touch down announced that the vis was greater than the RVR being broadcast. My client flew the approach and landed short of the runway by a couple of hundred yards. This was in the grass undershoot and there was no damage to man, beast or machine. However, the tyre marks were clearly visible. The CAA got to hear about it and the pilot was charged with recklessly endangering the safety of an aircraft. He was convicted of negligent endangerment (having admitted negligence during cross-examination) and was heavily fined.
The aircraft had flown a PAPI approach and there was evidence that suggested that these could become unreliable in the drifting low lying fog conditions that prevailed because of moisture refraction. This is particularly so if the PAPI's have not been switched on long enough to heat up and disperse any moisture inside the equipment.
As another contributor to the thread has already remarked part of the purpose of the legislation is that an apparently visual approach can be lost at a low and critical stage because of low lying fog/haze and the slant effect. This would appear to be what happened in our case.