I am better than average (possibly a lot better than average) at noticing that a baby is trying to talk, figuring out what they are saying and positively re-enforcing. It's not conscious, it's just how I am with babies, mostly because they fuss less if I can respond appropriately. Do I think of myself as hot housing learning to talk? No, I don't. I don't even think of myself as teaching speech. But the fact that I listen and respond to everything my kids say from babyhood probably has something to do with them being early talkers.
I like that analogy, it makes sense. I think you can probably only affect it within a certain range though, that they might be super early talkers because you did that, but without it they'd still be early talkers iykwim.
I was thinking about how my oldest two learned colours. If you'd asked me, I would say my DS1 knew all his colours fairly early, without me teaching him. Then I thought about when he was a baby and how he would only be happy in the pram if he could hear me talking, so I would talk and talk as I walked and a lot of of what I said was about the cars we were passing. "Here comes a blue car, and there's a white one parked there... blah blah blah..." I wasn't even thinking about teaching him colours, I just ran out of stuff to say! I think that's probably where he learnt it.
I didn't do that with my second, and he didn't know his colours as early has his brother. But then he was sent a colours workbook from his grandmother and he really wanted to do it. Within two days of getting that he knew the colours.
