Yeah, it’s not very clear to me either. From my reading, the poem is comparing the overwhelming majesty and elegance of the natural iceberg to the comparatively shoddy man-made vessel. But it’s open to interpretation.
The author definitely doesn’t do themselves any favors, though, by making an analogy with a fairly obscure poem and not even bothering to explain it.
After reading the poem, I agree that it's open to interpretation, but I also wonder whether the author of the linked article has really thought about what the poem means.
As far as I can tell, the poem seems to be about how icebergs exist in some majestic perpetual space of recurrence. The first stanza talks about how icebergs are impermanent, melt and eventually turn into rain ("Are you aware an iceberg takes repose / With you, and when it wakes may pasture on your snows?") but then the last stanza talks about how they perpetually arise again ("Like jewelry from a grave / It saves itself perpetually").
If anything, the poem seems like it would be perfect for referring to America's perpetual capacity to reinvent itself -- i.e., areas may fall into decay but then are rebuilt, much like urban Detroit is enjoying a revival -- not the more pessimistic take of the author of the piece.
The author definitely doesn’t do themselves any favors, though, by making an analogy with a fairly obscure poem and not even bothering to explain it.