I don't think its that uncommon. I used to do that as a kid (chew on the front of my shirt), and have seen some kids do that too. I'm not really sure why I did it and now when I think about it my front teeth feel sensitive and it kinda makes me lightheaded/nauseous (I imagine its the same thing as when some people hear drills and their teeth hurt).
He may not have sensory issues per se, but it could be a sensory thing where it gives him comfort to do that because it has a similar texture to his lovey. He's probably so used to his lovey being his security blanket that it has become a nervous habit to chew on something. So when he is without it he will try to find a substitute, even if it wasn't this it would probably have develop into another habit like sucking his thumb, biting his nails, or chewing on something else (pencils/pens, toys, gum).
He will most likely grow out of this phase but it may develop into another habit such as nail biting, face touching, finger/joint popping, or other types of fidgeting. Maybe you can try to find another outlet for his nervous energy- like having a little note pad he can carry around and doodle in when he feels nervous or one of those bubble pop key chains
http://thatslikewhoa.com/popping-bubble-wrap-keychain/