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...
I don't think it was a confirmed story. That is, the tiny "grain of rice" size Ethernet module that CEO of a security audit company allegedly found, was not present in other SuperMicro servers. SuperMicro itself, as well as it's buggest customers did not confirm the findings.
From what i recall, the story was very vague, there were no pictures of the specific chip, no pictures of the motherboard of the motherboard that would include serial, i.e. no details that would accompany a serious security research.
Did they originally say it was a grain of rice Ethernet module?
I thought it was supposed to be an incredibly tiny micro sitting on the bmc's boot flash to break inject vulnerabilities.