I think you are in good company when reading the accounting and seeing this as the point where it all broke down. Everything was reading very well, competent and conservative. Skipper comes up, likely tired, has not been experiencing the conditions long enough, has the forecast he's been sent by the router in his head; single reef. I immediately thought, it's dark, why not two with the stay then retire to a very quiet boat after under powering?3. On the accident night, the wind is described at about 2200 as increasing to 25 steady with gusts to 30 - and the response was to put in a single reef. The account is not specific on point of sail, but it sounds like the wind was behind the beam. My best practice on my boat is to look at the TWS and canvas the boat the same upwind or down, though I’ve certainly bent my own rules. It’s seductive to carry more sail off the wind - the boat isn’t heeling as much (none in my case - cat), the apparent wind is lower, the noise is lower, all the signals say the boat’s OK with the extra sail. Going to first reef and apparently still flying the genoa in that reported TWS I would consider overcanvassed in my boat. I think this is a critical point in the chain. This was an opportunity to go direct to second reef and downshift to staysail. Connection here to the local knowledge issue too….
I'm betting a combination of the forecast from the router and coming up in the dark, still foggy, led to the decision. Even good sailors make mistakes.