Pichu did not exist until Gen II, so that would be impossible. If you are asking why wasn't Pichu a part of Gen I, Maybe the idea of baby Pokemon came later on. Or maybe Professor
Oak could not find a Light Ball.
Level 26?? Pichu evolves into Pikachu when he has maximum happiness. Pikachu could have been Level 2. However, this is irrelevent because there are no such things as Levels in the anime.
As for the ball, it just looks like a Pokeball with a sticker on it. Maybe to identify it as the one containig Pikachu. There is nothing about it online, this was just my guess.