As a largely self-taught player, I learned to play octave chords by fingering one fret with my index finder and muting the next string by covering the next string also with the index finger.
A friend saw me doing it, and told me I should be using my middle finger to mute the string. I think as well as it works, either technique is valid. Am I right?
If it works for you, it works for you. There isn't a "correct" way, really.