They aren’t including payroll tax, just income tax.
"If the House GOP tax plan becomes law, nearly 81 million Americans 47.5 percent of all tax filers would pay nothing in federal income taxes next year"
So my point stands that you get ~80% of people still paying federal taxes (payroll and/or income).
https://www.washingtonpost.com/news/wonk/wp/2017/11/09/nearly-81-million-americans-would-pay-0-under-the-gop-tax-plan/