In the world of D&D there is the classic alignment chart: (Good, Neutral, Evil) X (Lawful, Neutral, Chaotic). In that world though you can be a Dark Mage but on the side of good.
But people misunderstand dark mages to assume they are aligned to evil.
On one hand, you had the old knight who understood correctly that a dark elf, living in a dark forest can be neutral.
Then you have the young inexperienced knight who thought that all dark elves must be evil aligned.
In the "system" of the manga, you can be "The Evil God" and "aligned evil" but according to the alignment be "neutral" (as the MC is). So it looks like "evil" is used doubly in this manga to refer to "dark" AND to "evil". The confusion is intentional to add uniqueness.