Bi Kai is not a frog looking at the sky from the bottom of the well; he's always willing to ask questions when he doesn't understand something.
Paul couldn't communicate with him, even with willingness, crafting techniques couldn't be explained in a short time.
So, much of the knowledge Bi Kai had to acquire from Chen Zhou.
After spending considerable time together, due to the shared linguistic roots, his Mandarin had become quite standard. Except for some terminologies that required Chen Zhou to explain, he could understand most concepts.
Regarding materials science and forging, Chen Zhou had both the theoretical knowledge from school and the practical experience accumulated from forging on a deserted island. His explanations were quite detailed and easy to understand.
With such a "teacher", Bi Kai came to understand why metals are hard, why they are strong, and why they do not corrode.
Why Treasure Swords can cut with a hair-thin edge, why they slice through iron like mud.
