If they wanted to cut ties for a different reason, execs could have just said "find a problem with some supermicro boards, no matter how much it costs to do so, and never repeat this conversation". They are complicated human-designed and -made artifacts; of course some problem exists. This is known in other situations as "parallel construction".

hard to believe the companies are knowingly lying.

If you're working with the feds on a national security incident, and the PR department comes round because some reporters were asking about it, the correct answer is "I don't know what you're talking about."