Here’s another angle: Not all of Greenland shows on the map. Therefore, it cannot be said that All of Greenland is contained within the Sea Zone. That’s the angle of thinking of the real Greenland.
The other angle, viewing Greenland as it is indicated in the fictitious world of the A&A board, would say that the only part that matters is the A&A version of Greenland, which only borders 1 seazone.
Here the standard rules become relevant: a sea zone does not include the land territory within it - they are two different zones. The Seazone does not continue along the map edge behind Greenland. Thus, the sea zone around Greenland touches the map edge at two points, one on either side of Greenland, like a horseshoe.
A horseshoe is not a closed shape. Therefore, the sea zone does not enclose Greenland.
Also, I think it’s the size of Greenland more than the fact that it is not in the Pacific that speaks against it. I realize the rule says nothing about size, but it fits the backstory of bases on small islands.
But it’s still a dumb rule. Planes can land on any island. Therefore, each island must be assumed to have an airbase from the beginning. It doesn’t take a move to move from in the air in a sea zone to landing on an AC in the same sea zone. And it makes no sense that it takes the same # of moves to fly through a seazone and land on an AC in the next seazone as it does to stop and land 1 seazone earlier.