It sounds like he is implying a back door, but in another post he said "it's no one's business" which seems hard line enough to imply there is not a back door.  "Not to the public anyway" could also mean he does not expect their methods to be susceptible to common methods of discovery, but that he would not rule out the NSA or IRS from figuring methods out.  He is very much into the details of crypto and is NOT quick to say "no one can break this".