From the Maui news article: "The cabin filled with "foul-smelling, thick smoke," and alarms blared while the crew searched frantically for the fire..."
If this is an accurate report, then one needs to wonder why the plane did not descend. If accurate, then this was a scarier incident than it seemed from the scant info on the initial reports.
What would descending accomplish? If the smoke was thick, it would bring you closer to the water you can not see. Descending would make the diversion take longer, and if you had a fire descending would increase the partial pressure of O2 to feed the fire.
The only reason I see to descend is if you thought you were in need of ditching and if you can't see out the window due to thick smoke, well it most likely won't be successful. Run the Cockpit Smoke/fire/Smoke evacuation checklist...then descend when you can see where you are going.
I'm sure they were running the qrh and if it said descend they would have.