While you are 100% correct a very simple counter example to the op that a lot of people have likely heard in their life is someone tuning a guitar. It would have saved me a lot of time if people couldn't tell the difference. :D
You can test this in the Vienna museum of music. There is a live demonstration with a headphone and with two knobs for the frequency of two separate tones playing together. Also, it visually shows the pitch of those two. If you go below the 12 tone pitch you hear only one tone, near the 12 tone pitch this one tone becomes suddenly to two separate tones.