Your anecdote seems to support that it’s a learned behavior/skill, which tracks for me. I have a very active internal dialogue that’s difficult to turn off. I say dialogue instead of monologue because I often make up “other voices” that bounce ideas off each other, and this generally happens without my conscious effort. I think I developed this because as I was growing up I was encouraged to pray regularly, and I was very fanatically religious as a kid so I did so as often as I could. I prayed silently so often in fact that my thoughts were basically a constant one-sided monologue directed to god. Whenever I would daydream or let my imagination wander I would imagine god responding, and eventually the constant monologue became a dialogue. I would work out problems or make decisions by having conversations with an imaginary god. When I stopped believing in god the second voice never went away, I just started recognizing it as my own.