I think the Los Angeles Times has good info since they're right here in SoCal and are reporting directly, not reading the AP news feed.
As such they are reporting 2 exits from the bunk area, one of which is also the entry. That and the hatch mentioned both open up to the galley and mess area and NOT to open air. So, apparently that's where the fire was concentrated trapping all below.
I can't imagine this really being the case because that is the ultimate in stupidity in marine design. And if true, lawsuits will abound.
Here's a snip from the article:
"When the fire broke out around 3 a.m., five crew members on deck jumped overboard and escaped, paddling a dinghy to a nearby boat. Everyone else — including another member of the crew — was in sleeping quarters below deck and unable to get out, with the only two exits apparently blocked by fire.
Santa Barbara County Sheriff Bill Brown said Tuesday that the victims were trapped below deck with no way of getting to safety.
“There was a stairwell to get down the main entryway up and down and there was an escape hatch, and it would appear as though both of those were blocked by fire,” he said.
The main staircase led into the galley, and the hatch opened into the adjacent mess area, both of which were engulfed in flames."
Link but you might need the subscription.
https://enewspaper.latimes.com/desktop/latimes/default.aspx?edid=ac3dde94-06c8-404f-8095-7a94cba03896