This isn't really a gray area. He stole a bunch of documents on the way out, founded a new company based on IP he didn't own, and then sold it to another company. (assuming google's allegations are true)
Well, the evidence that Google has gathered to suggest that Levandowski did copy the documents and then tried to cover his tracks is pretty persuasive, so it might be safe to assume that part of it is true.
However, whether or not he used those documents in an inappropriate manner in Otto or Uber is still up for debate.