First, I'll say it is pretty common to use the terms interchangeably. I don't think anyone was confused by what I wrote, or that your "clarification" was in any way helpful. See, for example, these legal groups using the term "protected group" in relation to US employment law:

* https://www.osbar.org/public/legalinfo/1095_DiscriminationEm...

* https://pedersenlaw.com/practice-areas/discrimination/

Secondly, I used the phrase "protected group" referring to disparate impact, and here, your assertion (to the extent it has any validity at all) is simply incorrect. The entire idea is to ferret out subtle acts of discrimination that have an outsize impact on a group consisting of members of a protected class, and in the case law you see the phrase "protected group" used explicitly. For example:

  On the contrary, the ultimate burden of proving that discrimination against a protected group has been caused by a specific employment practice remains with the plaintiff at all times (Watson v Fort Worth Bank & Trust, 487 US 977 - Supreme Court 1988[0])