[horsawlarway]

He's using a specific legal term in the US.

See: https://en.wikipedia.org/wiki/Protected_group

A protected class is a group that is illegal to discriminate against in this manner, in the United States (and several other legal systems).

"Phone OS" is not a protected class. Many other things are, though, such as Race, Religion, Sex, etc... Varying a bit by jurisdiction and legal system.