I'm reading a book and don't understand what the author means by "twenty-word master-class" in the last sentence of the paragraph shown below. Does "twenty-word" have any other special meaning in English world? Or it just simply means "20 words"?
"The American writer and graphic designer Nancy Duarte worked with Al Gore on his storytelling technique in the movie An Inconvenient Truth (2006). Duarte calls rhetorical tricks like Campbell’s jokes a STAR moment, ‘Something They Always Remember’, and when I talked to members of the audience afterwards, they certainly did remember Campbell’s anecdote about being ‘evil’. It was a twenty-word master-class in communications."