Is that the normal way of performing VFR flights at night in the US? “follow the shoreline northbound at or below 500 feet.”
I've had that clearance a number of times following the Florida coast. As said, it keeps you under the approach path. One flying just offshore of Miami Beach, I was instructed to fly at 250 feet. I asked for confirmation, and the instruction was confirmed, so I did. The only option, would be to fly far off shore, which is undesirable in a single.
It sounds like the pilot was initially headed south[east] bound from Lantana airport, planning a left/northbound turn at the shore. Once the pilot crossed off shore, on a south[east], turning to north heading, there would have been no surface visual reference, only ocean. At night, this is no longer effective VMC. Perhaps a similar event to JFK Jr.