To an extent that's true. But the more general question is Where in Scripture does Scripture say what Scripture is?
And the answer to that question is: nowhere.
Scripture speaks highly of Scripture, but it doesn't give a list of what counts as Scripture.
If we remember that in the ancient world, not much was written, and the farther one goes back, the more true that is, the fact that the word "scripture" simply means "writing" in Latin is indicative of the importance that ancients in a mostly-illiterate society placed on writing.
We attribute supernatural power to Scripture, as did ancients such as Paul. Scripture is very important, according to Scripture. But Scripture doesn't spell out what IS Scripture, and the different Christian churches disagree as to what is actually IN the Bible. In the end, the answer is that "Scripture" is whatever your church says Scripture is.
And that means that Enoch, Jubilees, 1,2,3 and 4 Maccabees, Wisdom, Sirach, Tobit, Judith, two different versions of Esther, about a third of Daniel, the Didache and some other books I can't think of right now either are or are not Scripture depending on the denomination of the believer.
And then, among the books that everybody agrees on, the question of what is TRUE scripture comes down to certain manuscripts, with some recognizing certain ones as the authentic Scriptures, while others reject those manuscripts in favor of others.
Never mind translations thereof, which adds a whole level to complexity.
So before anybody talks about the authority of "Scripture", it can be useful to know exactly what is and isn't Scripture to that person, and why they think that. It gives a good insight into his or her thought processes on the subject.