During the storm captain promotion cutscene, the NPC says,

Quote Originally Posted by Slafyrsyn
For outstanding efforts in the Adventurer Squadron initiative, Captain Surname is hereby promoted to storm captain.
At least in the US armed forces, a promotee is called by the lower rank up until "promoted to" or "authorized to assume" the higher rank, e.g.,

Quote Originally Posted by Expected
(First) Lieutenant Surname is hereby promoted to Storm Captain.
as you wouldn't promote a captain to captain.