In the U.S., there is a very high bar to accuse defamation. You not only need to prove the report is false, you also need to prove the reporter knew it was false and had bad intention to cause damage.
From my lay understanding, Supermicro has a slam dunk case given the impact on their stock price.
At least in the US, I don't think this is true. Defamation is a broader class that includes libel, and always requires proving that the publisher was at least "negligent" in publishing the false statement: https://www.law.cornell.edu/wex/defamation