The first person POV of telling a story is by using the words I, we, my, etc. in the point of view of the narrator. This way of story-telling can be written in a variety of ways such as a first person protagonist, first person witness, re-teller of a story in first person, etc. Therefore, it is true that most authors who write in first person use the protagonist to tell the story as this is very much possible. Even I have written a couple of first person point of view stories as the protagonist!
I hope I was able to satisfyingly answer your question. Good luck! :)
