The phrase "actively doing anything" is too slippery. What one person does passively another may do actively. People who post on Less Wrong tend to do things consciously more often than the general public. The theories which say that children acquire language without anyone doing anything special are no doubt studying the behavior of normal people.

The conclusion is that Viliam is probably simply thinking out loud about things that most people consider only subconsciously and implement in some way but don't know how to articulate. If you try to acquire a foreign language by merely listening to native speakers converse, you will learn very little. Children learn language when adults adapt their speech to their level and attempt to bridge the inferential distance. Most people do this by accident of having the impulses of a human parent.