Apprentice Blacksmiths are unable to create items of their own devising in Rise Online, so it is only possible to forge something if they have a completed diagram or a tutor.
This is why Kaizen, despite being a complete novice, was able to complete a Swift Arrow. Therkara Ironstone was tutoring him.
Yes, he refined the final item a bit by including unconventional methods, creating a better item than his master thought possible. However, this only happened after he had already learned the basic diagram of the Swift Arrow. The profession's system does not prevent an apprentice blacksmith from perfecting something that already exists.
Unfortunately, for Kaizen, the day off when he would be able to create a completely original item was still far away. He needed to learn a lot about his profession before that happened.