Confirm a pending user, confirms?

I am looking for info on whether the Atlas function to Confirm A Pending User actually confirms a pending user.

There are a couple of questions about this on the forums and the general gist is that the user must log in the first time for their status to change from Pending to Confirmed - our testing shows the same but is this another option?

This is the post endpoint{groupId}/apps/{appId}/user_registrations/by_email/{email}/confirm