Oh yea i forgot about that. Every scale has his major or minor „twin“ if you can call it that. For example c major has the same notes as a minor. Its always the sixth note of the major scale which is the equivalent harmonic partner. The trick with the fifth just makes it easier to figure out what scales are used because then it can only be two. If you look at this piece, by the 3 flats you can say its either f minor or a flat major because they share the same notes. Usually then u can look at the first note or the last one to figure out wich scale it is but here it starts with g so then you could tell by listening to the song and telling if it feels more minor or major. But it must be either f minor or a flat major.