Thanks for the link. I agree - something you might not see today not only because TV shows might not want to do something like this but also because few composers would be comfortable with having an audience laugh at their performance. You can’t convince me that he didn’t know people would react that way. At least nobody cried.
As is evident in the linked movie, Cage had a zen attitude towards his public's reaction. No problem if they preferred to laugh, cry, of show interest. He had to create the event, just for the joy of donating something to the others.
Once I saw a documentary, made by the Italian TV in the late Eighties, called "John Cage e i bambini" (start from "http://cezanne.psice.unibo.it/cde/ricerca.asp" to read the data). He did a show with school chairs and acrylic flooring, at the benefit of the children. A very delicate moment, that was interesting both for the piece, and for the children's varied reaction to the strange show. Cage appeared seraphic as usual, and looked as a child among children.