Here's the context of and footnote in question -- #3, after the first sentence in the last paragraph of LeWitt's very short essay:
"These paragraphs are not intended as catagorical imperatives but the ideas stated are as close as possible to my thinking at this time. 3
3 I dislike the term 'work of art' because I am not in favor of work and term sounds pretentious. But I don't know what other term to use."
You'll notice almost immediately that there is not a direct correlation between the context of the footnote and the footnote itself; the term discussed -- "work of art" -- doesn't appear in the referring sentence, but it's not hard to see the footnote as a clarification as to why he doesn't just call "These paragraphs" a "work of art". It's the cognitive leap we make in that correlation that allows the essay to transform into art rather than prose because the full scope of its purpose is never made explicit. But a clue to its scope is embedded right into the form. Take that modernism!