Rodolphus did not stop when the whirwind took hold. But then he felt the pull against dark magic. It was the precursor to something that he'd only ever felt twice before in his life.
The last time he'd seen fiendfyre used, it immolated not only every single living and non living thing in it's path, but the caster obviously didn't know of the ramifications of such dark magic. Nobody cast fiendfyre and lived long. Well, if they did, it would take such a toll on their magic, many ended up as squibs.
Antonin must have been desperate to save himself to resort to such measures. But Rodolphus was no fool, and did not stick around to see the end result of such madness. He apparated away, to the complete opposite side of the field.
And Antonin called him the madman. Only one such as that - and with the arrogance that only came with madness - would think to call on the elements to retcon a person's existence. As he apparated away long before the heat of the flames could get near him, he agreed that Antonin had always been a fool.