He is the other rookie because any defensive lineman in the same draft class as Abdul Carter is going to get second billing. That is just the way it is and the way it is going to be.
This does not mean Darius Alexander will have to spend much time on the side, watching the uber-impressive Carter do his thing, presumably from Day 1 as a key figure within the Giants defense.
When training camp and the preseason games are over and done with, there is every reason to believe Alexander will be a significant part of the line rotation and quite possibly a starter alongside Dexter Lawrence.
That would thrust Alexander into a spotlight he doesn’t crave.