The interview posted many pages ago said there were no doors which is what I was going off of. I understood there was a way to secure the boat when nobody was aboard. I would be surprised if the COI allowed those "doors" to be used with passengers aboard. Or that anyone would close them at night at this time of year.
I know everyone is focused on lithium batteries but the galley was all electric, plus I understood the generator ran at night. Plus electrical fires are statistically the most likely on any vessel. A wiring issue behind a cabinet (similar to the fire described by @Wookie
on his vessel) could just as easily smolder until it flashed over. With windows and doors open, a photo ionization smoke detector not picking up smoldering smoke even under the best of circumstances, it's not implausible that this started entirely independent of any lithium ions or chargers.