Sort of, but not exactly. To be more accurate, the Ford 6.4L was a derivative of a new International truck engine and the first commercially available version of it, but Navistar always had their own version for the medium truck market under their International label (later named "Maxxforce"). The same was true of the previous Ford Powerstroke 7.3L - it was a derivative of an International 7.3L diesel.
The Ford versions were tailored for the Ford pick-up truck application and used some Ford components outside the basic engine block. When most of us talk about an engine, we mean the whole assembly, including fuel supply system, cooling system, starter motor & wiring, and exhaust headers. However, those external components are typically tailored for each application of the basic engine, so there are often noticeable differences.