I don't think that is really misleading, at least I wouldn't consider Medicare/social security as a part of my federal income tax. When I think of income tax I think of tax brackets and deductions, not payroll taxes which are deducted before I ever receive any income, and which I never really have to deal with.

Based on the headline, I would have assumed that 57% of people had enough deductions/low enough income to be below the bottom income tax bracket. Which is correct, based on what you said.