No Kracken, whether he knew about a law or not, his actions were incredibly arrogant and reckless. The only plausible other explanation, is he was not paying attention and didn't see you. Doubtful, but possible.
I would put the cruiser's captain in the Careless and Negligent department. Just think of the possibilities if he had headed straight towards you and did the same
Another case that I use to buttress my claim that the MP should provide for "floating" patrols (no silly pun intended). Have a couple of MP boats, unmarked if possible, that do not have the assigned drudgery of pestering people for boarding, rafting, whatever. Their focus is on boaters like your cruiser story, NWZ violators (real fast), dangerous tubers and the like. I know they do this from time to time, but not the same as a moving craft covering lots of water throughout the day.
Maybe El could chime in here and offer more suggestions as to how best handle these ongoing problems. I simply don't know another way.