i'm pretty sure it was that the hughes brothers promised him the lead role when they were pitching the film to garner more interest from studios (because Pac was already a relatively big name at that point, and studios obviously want a big name attatched to their projects), but once the hughes brothers secured a deal, they re-cast Pac as either O-Dog or Sharif (judging by that allhiphop interview, i'm guessing it was sharif). So understandably Pac was upset over his name being used to sell a film and about being bamboozled by the hughes.