Because that was a game, this is real life (well in the bl) and he reincarnated as a side character with minimal info in the actual game not as one of the main characters ofc he wouldnt know a random patient or all the patients the character he reincarnated as treated
he had to be taught the concept of dungeons & about the enemies in low-rank dungeons. how did he not come across that while playing the game
like idk, maybe the genre of the game was a visual novel or something and not a game with actual gameplay
Keep in mind that he also transmigrated after the end of the game and beating monsters in a game is so much easier and safer than in person experience.
im not arguing that fighting monsters should be easy, but he should still know what they are, shouldnt he?
why is he so clueless? didnt he play and beat the mf game??