This character is or seems ignorant and lacking common sense.
Ignorant characters are unaware of most things that are considered common knowledge by regular people. It is not because they are incapable of learning, but usually because they just never got the chance to learn or didn't try.
They don't understand the things that are considered obvious by most people because their thought process is different doesn't usually end with the same results with others.
Their actions might seem stupid, meaningless and outright wrong, but that doesn't mean that they are stupid, cruel or evil, they are usually just different.
An ignorant character may be from a distant place or time or maybe he/she just got out of prison, or returned from a prolonged conflict.
An ignorant character is different from an uneducated one since it is not about education. Though a character may carry both of the traits.
No Common Sense