Personally, I think Bernie is the next Madoff and electing him President will usher in 10,000 years of death and darkness (unless you are a white, male, college student -- P.S. plenty of time still left to get a sex and skin change operation as well as to go back to school), but even I think this is a misleading interview.
Did Obama know exactly how he was going to close Guantanamo Bay? No, and maybe he still doesn't. The President is not a dictator, but he does have a large amount of influence. He can appoint a committee. He can help introduce and sway legislature. He can bring members of Congress together.
I think Sanders is saying, in very literal terms, that he doesn't know which option will be the best. I don't think anyone does until the election is over and we can take stock of the new political landscape. If he says, "We're going to write Bill HR012 and I'm going to talk to these reps in order to get it passed" it will become political fodder immediately and will be used against him by any- and every- one. For now, it's enough that he says he will make it a priority of his first year in office. In some ways, that's really what a President's job is: to set priorities.