He sounds just like my cat. KC will walk up and chomp on your leg for no reason other than you walked into the room. She is a fixed, well exercised cat with all the room she could ever need/want to play. Her bite has softened over time to a point I can live with it (it's actually quite fun to play with her).
Not sure if you can do anything about the behavior or not...best of luck.
Here's my pride and joy doing what she does best...
