What? No, you said it, the ear splits the sound into frequencies and physically puts sensors into places where they resonate. Octave resonates in the same place. (but higher octave resonates in one additional place)
The higher tone also excites the sensors for the lower tone.
Wait, does it? I might be spouting bullshit, sorry.
Thinking about it, I'm not so sure it doesn't. I'm not a physicist to know it for sure.
The octave rule definitely has some physical/biological founding, it’s not purely cultural. Although culture also plays a role in its preponderance.