The patent is ATEBITS LLC's, and I understand Atebits is now a subsidiary of Twitter. So the patent would indeed be Twitter's, Loren is listed as the inventor but is not the assignee.
He probably shouldn't have been promising not to use a patent he didn't own anymore, then. Not cool, unless there's a private agreement requiring his consent for patent usage.
Either this, or negotiated/set a better expectation that he isn't going to bring certain inventions with him to Twitter. Granted, this probably would have made it harder for an agreement on terms regarding his place at Twitter to come into existence.
