"Kaito" is a standard generic Japanese name.
It was chosen because it matched the name of "Meiko", because Kaito was her counterpart.
Its only since the CV series have been shown in Vocaloids have been given names with intended meaning. And even then not all have meanings to the name, particularly with Spanish or English ones as their names are chosen normally as per standard. However, oddities like "Prima" (from "prima donna") and "Sonika" (Hindu name meaning "Golden") exist. Most of these like "Leon" do have particular meanings and word origins so you can find their meanings in a baby name dictionary, properly can do this also for the Japanese Vocaloids too.