I think you're correct, kalmisto, I doubt he knows all the grammar rules, he just speaks.
As said before, IMO the key is to learn Finnish grammar for 6-18 months, then just try to speak, listen, and speak again. Then do that for 4+ years and you're there!

English is a language that can be learned with only very basic grammar, whereas in Finnish you need fairly good grammar before you can break an unknown word down into it's basic form so you can look it up in a dictionary.
I really admire Neil, Roman, Keke, etc, they are "true integrators"!
Political correctness is the belief that it's possible to pick up a turd by the clean end.