Having the hype to see it on IMAX has sure helped, as those tickets are like double the price, therefore bringing in a lot of extra money.
Also, his claim that he recreated a nuclear bomb scene with no CGI has also interested plenty people to check it out. Myself included.
Christopher Nolan's track record of well made films that get rated pretty high has also helped.
Had this been from a no name director shot digitally, or even on typical 35mm film, but basically the same movie, I don't think it would be doing even close to as good.
Of course you would get the history people that want to see it and know the Oppenheimer story, but those people wouldn't be near enough to bring in these type numbers.