I don't know exactly what Amazon asked for in this case, but any time for me in the past at either school, work, or otherwise, when "doctor's note" is mentioned

I don't know exactly what Amazon asked for in this case, but any time for me in the past at either school, work, or otherwise, when "doctor's note" is mentioned, they aren't asking for a definitive diagnosis. In fact, I've never even seen a doctor's note that specifically said "[name] has influenza/rhinovirus/UTI". It's always been sufficient for the note to just say something like "I am a doctor and [name] was seen by me for digestive tract issues, please accommodate them." I can't imagine that wouldn't have sufficed here, too.