"...was discharged roughly three hours later after being diagnosed with an “influenza-like illness” despite testing negative for the flu, the lawsuit asserts."

This makes it sound like testing negative for flu should have precluded a diagnosis of influenza-like illness. But influenza-like illness means an illness with similar symptoms to influenza, not necessarily influenza itself. That diagnosis was wrong, and the wrongness of the diagnosis was pretty clearly the result of medical error, but the wrongness had nothing at all to do with a negative influenza test.