LORE - Question on Knights-Errant and Witch Hunters

[𝓐𝓷𝓰𝓮𝓵]

So I just got to the part of talking to the three crones in the swamp at the orphanage. And when they say that they want you to get rid of a dark power.. why does Geralt say they should look for a Knight-Errant or Witch Hunter instead of a Witcher. Sorry if I'm missing something obvious. I've tried a few google searches that didnt turn up much lore on those two factions/character types.

[HoarseHed]

Mostly because witchers deal in curses and monsters/specters. Not in dark mystical powers that be, or angry gods or goddesses. Witch hunters and knight errants would be more fitting for quests like that. Mostly just him be defiant.

[Terminal Frost]

Witchers hunt monsters and deal with the supernatural. Witchers are superhuman mutants created through magic. Proficient in multiple weapon types; carry silver sword for fighting monsters.

Witch Hunters are humans trained to hunt witches, sorceresses, and mages. The use steel swords. Also, known to use dimeterium to counter magic.

Knights-Errant are essentially travelling knights who do good deeds to help out damsels in distress and local populace that is being oppressed/terrorized...though, in reality, they probably just do such acts as a way of making coin while not in the employ of a lord/king/army...