How to deal with papers/authors that provide no details of implementation?
In your thesis, I think it should be safe to say something along the lines of 


  "John Doe et. al. claim in [22] that the algorithm would run 400X faster with their implementation, however, the details are unclear."


and leave it there. If you are asked more about it in your defense, you may politely state that you tried to approach the authors for more information but could not get it.