Arthur could sense that the boy was at the first transformation of the second mortal coil. So he had just transcended the first mortal coil after five years of being a disciple of the sect.
This performance isn't because the boy slacks off. Arthur knows that the boy does slack off in cultivating and focuses more on tinkering with forging. But the main reason why he is just reaching the second mortal coil now is because he entered the sect at the eighth transformation of the first mortal coil.
This boy had participated in the regional sect examination to try his luck. He didn't have much hope because he came from a poor background and was weak, but it was discovered that he had a bloodline that helped him sense and identify the properties of metals.
After his special ability was discovered, he was singled out, and his examination was interfered with to protect him.
