You can see just by that link that the link itself is confused. It begins:
> [A Protected Class is] A group of people with a common characteristic who are legally protected from employment discrimination on the basis of that characteristic.
You'll immediately notice that "women" are a group of people with a common characteristic (sex) who are legally protected etc etc. "Sex", despite being listed further down the page as a "protected class", does not meet the definition, as sex is not a group of people. Rather, it is a characteristic which federal law protects.
Women are not a protected class. Sex is a protected class.