He didn't say he blew up a nuke, just that he recreated the shot. At most, he could have used a ton of conventional explosives which can create a mushroom cloud-like effect. Or he might have just played a lot of tricks with smoke machines and lighting.
There's a million obvious reasons to know he didn't use a nuke, from the fact that it would be impossible to get one to the fact that it is against international law to test them above ground to the fact that the expense would be extraordinary.
Though if this motherfukker made some sort of deal with the North Koreans to film during one of their tests that would be GOAT-tier shyt.
that people really need to be told Christopher Nolan didn’t detonate an actual nuke