Are 501(c)3 organization meetings open to the public?

Answer 1

No. A 501(c)(3) can be just as "private" as any other corporatation; it just means that it's formed for a nonprofit purpose. Just like regular, privately-held corporations' books, records, and meetings are not open, a 501(c)(3)'s doesn't have to be, either.

Answer 2

Some states require charities to file reports with the secretary of state or attorney general to show how they spend the money they raise. Section 501(c)(3) is a federal law and it only requires that the organization operate for an exempt purpose.