The NCAA decided to call it a First Round to make money and because they plan on expanding it some more in the future, but by every meaning of the word, they are play-in games.
A true First Round would be rewarding the Top 8 teams a true bye for being so good during the regular season and having the other 60 play in the First Round. The way it is set up right now is play-in style and they call it the First Round by name but not by definition.