I don't see anything that says they died from exposure. Apparently the helicopter capsized immediately upon landing, which is pretty much expected in 9-ft seas. From the NTSB report, it's impossible to attribute the deaths to anything. I don't have access to a coroner's report.
Flying single-engine helicopters when the seas are high isn't the brightest idea anyone ever came up with, but it is unfortunately perfectly legal. Some judgement is required.