Ukulele is the easiest?

A day I found, that The American Music Conference declared that;

The American Music Conference announced in September 1977 that the easiest instrument is the ukulele, and the most difficult are the French Horn and the Oboe, which latter has been described as 'the ill woodwind that no-one blows good.

My Uke student found this footage on the Guinness Book of Records released on 1980-1988.

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So I have some questions now.

• In 1989, some musical instrument won the ukulele at easiness. Which was the easiest now?
  
• 1980-1988, ukulele was the easiest. I don't understand why the voice, the castanets, or triangle was not the easiest. Every musical instrument has original difficulty, for example, I can play piano and chromatic harmonica easier than Uke.
  

I wanna know some.