poisonous dragon and something like that title can only Be given to the patriarch of the tang clan/someone who achieve all poisonous stuff
Dragon can be understood as "best". Dragon is thus used for someone who is considered the best at something. So poisonous dragon = best at poisons. It is often used for the younger generation since they haven't properly established themselves yet. Flying dragon = a very promising new martial artist that is the best a flying within his generation. Once he is older he will likely get a new title that refers to either a defining event or defining feature/skill.
What with that epithet? Why are murim stories obssessed with dragons? MC is know for his knowledge on insects and poisonus creatures and they gave him "flying dragon"? Are they dumb?! At least make it poisonus dragon