I give SuperMicro the benefit of the doubt.
If the entity making a claim can not or will not produce proof of their claim, then the other party can legally sue for libel. If the paper refuses to produce one of the supposedly compromised boards, SuperMicro can take them to court & sue the shit out of them.
Because of that I'm siding with SuperMicro on this one. The paper either has to Put Up, Shut Up, or Get Sued. A full page retraction may be just the tip of the court ordered justice.