How could Rudy be a sorcerer before he was an adventurer?

Question

Heavy spoilers if you haven't gotten past the Return of the Goblin King arc.

Rudy was not an adventurer until after Shiroe successfully raised him using new world-level magic. How was he able to gain levels beforehand? Can People of The Land have classes and gain XP even if they are not adventurers? It seems to me that you have to be an adventurer before you can gain levels and things.

Answer 1

Landers (or People of the Land) do gain levels, but is very low compared that of an Adventurer.

As per his wikia:

He put tremendous effort into this guise; as a Lander, his EXP leveling rate was 1/4 that of an Adventurer, yet he was able to achieve a class level similar to beginning adventurers before his status change