I'm not sure whether an HQ, being in a port 2 hex away from an enemy air unit is in supply or not (of course no friendly ZOI in the area)
In other words is the water hexside of the port hex considered an "un-neutralized ennemy ZOI hexside"
If it is an island then you are OOS. There are situations where a port is on the mainland or a large island, such as New Guinea, where the HQ may have an overland supply line to another port that it can trace out of, so it depends based on how the question was worded.
The simple answer is if the HQ needs to trace through a water hexside to be in supply, in your example it would be OOS.