Impressive that his two professors took 1 whole month to finally believe him, even though the article gives the impression that the error was obvious (a bad formula).
I suspect that without their co-authorship people wouldn't have read it. I'm not in the academic field but isn't it a signal that they back his work enough to put their name (and reputation) to it?
Is it good for your career to get high impact factor for a paper that admits that your most famous work was a fraud that destroyed the economy of several nations?