Those claims were never confirmed, no? Some of it might be true or trueish but I'm not talking Bloomberg's anonymous sources word for it, and with so much supermicro gear out there you would think some other evidence would show up.
A supply chain attack similar to Supermicro's would be much more targeted and recalls with national security implications do get flagged via a separate chain.
It depends on what you consider confirmed. It was kind of corroborated, at least. There was a CEO of a hardware security firm that came forward after the original article. He claimed that his firm had actually found a hardware implant on a board during a security audit. It wasn't exactly as Bloomberg described, though.
His take was that it was very unlikely that it impacted exclusively Supermicro, though.
It was covered various places, including The Register https://www.theregister.com/2018/10/09/bloomberg_super_micro...