Maybe we can look at this in a different way maybe due to the fact if you take b6 you believe you have more chance lucid dreaming, so due to this suggestion that is will make dreaming easier makes you think you can more than without like a psychological thing.

Example- When i was a kid and i had a cold my parents used to say if you drink this glass of liquid your symptoms ill go and i believed it would work so i used to feel better but when i asked what was in the glass a few days later my reply was just water. So maybe its just the suggestion that it will help is all it is.