Operational Experience vs Manual Limits
PVTPLT,
Something to consider while you're learning: We weren't there.
If the fog was blamed, I have to assume they couldn't see the better landing options. Likewise, I assume they knew they were right at the limit for their slope limitations and chose to continue the landing. All that makes me think they were concerned that the fog was getting worse and were at risk of losing control of the aircraft. What I don't know is the particular avionics fit on that aircraft or the maintenance status, I also don't know if the pilot was already starting to experience spatial disorientation; all of which would play into the a decision to land vice perform an ITO, declare an emergency and fly home IFR.
For you to dig up a flight manual quote without asking about all the factors that actually affect in flight decisions shows your inexperience. In any event like this there is rarely black and white, things are mostly grey. At the end of the day, this worked out good. That doesn't mean there isn't learning to be had or things to do different next time, but hand wringing about unprofessional behavior based on what your non-flight approved GPS shows is not helpful for anyone.
I suggest you learn to listen more, speak less and ask questions from those more experienced than you before passing judgement. You may be on to something despite others experience, but you need to do the due diligence to make sure you're right before telling the emperor he's naked. When you don't, you get what you have here; the experienced folks ignore you.
Busdriver