Luther may have said something similar but the quote is from [WCF XXXI.3](https://opc.org/wcf.html#Chapter_31) - a Protestant "council," if you will:
> 3. All synods or councils, since the Apostles’ times, whether general or particular, may err; and many have erred. Therefore they are not to be made the rule of faith, or practice; but to be used as a help in both.
To understand what we Protestants (or at least we Reformed/Presbyterians) actually think about the question of conciliar authority, I'd suggest reading the whole chapter. It's not long.
The _Scriptures_ are inspired, inerrant and infallible; councils are not. Case in point: what did the 'Ecumenical councils' rule on the question of monophysitism? Which of the contradictory conciliar decisions is the 'right one' and on what basis do you make that determination? These councils have a derived authority "if consonant to the Word of God" - which means Scripture itself has primary authority. And that's what _sola scriptura_ is all about.
Similarly, to understand what we actually think about _sola scriptura_, read [WCF I](https://opc.org/wcf.html#Chapter_01) - in particular:
> 4. The authority of the Holy Scripture, for which it ought to be believed, and obeyed, dependeth not upon the testimony of any man, or church; but wholly upon God (who is truth itself) the author thereof: and therefore it is to be received, because it is the Word of God.
Authority is not _bestowed_ or _granted_ by men; it is _self-contained_ and _inherent_ and therefore only _recognized_. We would still have a Bible without the ecumenical councils, because Scripture is self-attesting and "his sheep hear his voice." And the vast majority of the Scriptures (the Law, the Prophets, and the Writings) were already long-established by the Old Testament Church (as organism) before the time of Christ anyway--the church (as organism) simply received them before any official 'stamp of approval' was declared by "The Church" (as organization).
So, where did we get our Bible? That's easy: [2 Peter 1:16-21](https://blb.sc/002Qik) (especially verse 21). And how do we decide doctrinal questions? By being like the Bereans, who received the word with all openness of heart--but then searched the Scriptures daily to see whether these things were true. In other words: "don't trust, verify."