I went and talked to customs the other day to get straight in my mind
as to aliens having to report in whenever they move.
The way it was explained to me is thus;
When you first arrive at a designated port of entry, you call
customs. They come to the boat and check your papers and ask your plans.
If you are sailing thru to another country or are going to make an
extended cruise along the coast, for instance, you check in at Neah Bay
and are planning to sail south to other US ports and then on to Mexico,
you are required to get a cruising license, which is free, and you must
call an 800 number each time you stop.
If you are say, a Canadian, and are down in the Seattle area and
going to bop around the Puget Sound area for awhile, no license is required.
It sounds like the chap on the east coast never informed customs he
was planning a trip up the coast and so he ran afoul of the law.
It is all up to customs to decide who needs what and what must be done.

Of course, this is customs and homeland security, border patrol is
another issue.