That's just a boat prop though; you can see them in various singleplayer scenes too. They've just made them move around on pre-defined paths as part of the background scenery, and in no way does that mean naval warfare has been implemented (or even worked on). The guy in the video just teleported players onto the boat somehow to show them off.
Where'd you find that number? Steam lets you sort reviews by hours of playtime at the time the review was written, and it appears only about 3% of people who reviewed the game had < 1 hour of playtime at the time of their review (3340 / 114394 = 0.029). I don't know how Steam counts people who changed their review later though.
There are quite a few more reviews from people with 100+ hrs playtime, and those reviews are actually
more positive than the ones with < 1 hr of playtime (85% positive vs 71% for < 1 hr playtime).
(Sorry for being kind of petty haha, 90% just seems way off base)