I rewatched the first episode of Voyager, and when Neelix first comes aboard the ship, he marvels at the great culture that created it. Tuvok says something along the lines of "The Federation is made up of many cultures. I am Vulcan". A few scenes later, Neelix calls Tuvok "Mr. Vulcan", and Tuvok does not correct him. So, yeah, 100% lack of communication on Tuvok's side. Sure, Neelix hears other people call Tuvok by his proper name, and as some point he understood "Vulcan" is the name of his race. But by then, as Tuvok never corrected him or shown any visible dislike to being called that, he might have come to the conclusion that Tuvok likes it, and thinks of it as a funny nickname.