It's what the taxpayer the article is written about is asking the Courts and IRS to define (i.e., are wages income?). He cites a case in the past were the court ruled that it wasn't income, because your labor is considered an expense to you.
I'm no expert in these matters, just trying to clear up what's being presented in the article linked.
Even if that was a legitimate argument how would he argue that he needn't file a tax return for any interest or dividends he received? At the income levels discussed in the article it's very likely he had some of that type of income. (I know you were just summarizing his argument, not necessarily agreeing with it.)