The government said that it could neither confirm nor deny that he was flying a MiG. To me it seems if he was not flying one than the communications team would decide simply to say so. The fact that there was ambiguity about it seems to suggest he was indeed flying a MiG.
While I don't know much about the crash and Robert Bond, I believe that through the small of research I have done, I have come to the conclusion that it's a very real possibility that Bond was piloting a MiG. The government has its secrets and every once in a while, they slip out.
This seems a conspiracy theory that, like so many others, can never truly be disproved. Why is it so improbable that the military would have acquired in some way or another a Russian MiG? And that if they had, they would have undoubtably needed someone to fly it to learn its capabilities.
I do not believe Robert Bond flew a MiG jet fighter. There are a lot of costs and logistics to supporting the operation and maintenance of a modern jet fighter. Typically only governments have the resources to be able to pay these costs. In addition Robert Bond is very unlikely to have the required skills or training to pull of this feat.