I think it's the dex and the professors- as a kid you go in with a blank slate and have the best advice there is. Most people probably train by weird old wives' tales like 'don't get flirty, evolve by thirty', things that don't actually work. They're telling you what a pokemon is because you might think you already know.

 

Well, traded pokemon do grow faster with the other trainer. Perhaps it was observed that out-worlders are the ultimate example of this phenomenon.