Bernie Sanders is suggesting that charter schools have their federal funding and scholarships frozen. However, charter schools are funded by the public school districts, which means federal funding would freeze for public schools. In essence, a charter school is a public school, just with their own management and rules.
Technically speaking, freezing federal funding for charter schools is freezing federal funding for public schools.
If Bernie Sanders says this differently, such as "stop giving money to charter schools out of public school budgets" then it would make more sense.
Either way, he's attacking education and the parental choice to send their children to schools they prefer.