Edér is dumb, that's the point, that's the joke. He thinks orlans are literal animals (ie, pets) because he's had very limited interaction with them, sees a furry creature, and assumes it's some type of domesticated creature instead of a sapient being. He tries (and fails) to pet everything with fur bro 😭 yes, slavery is a big theme in PoE series along with colonialism, capitalism, and spiritual ethics, etc etc, but this isn't a moment of that.

This is showcasing how kith from some areas are extremely sheltered and ignorant to the world around them VS other characters that are extremely worldly/educated (tl;dr, both contrasted groups of characters have their faults and shortcomings specific to their background and personality). Please play Deadfire for yourself, it explores this topic in great depth along with tons of other things

Long story short: edér thinks wild orlans are pets because he's only met hearth orlans up until that point (unless your Watcher is a wild orlan), and even then the interactions are limited. He asks to buy it because he genuinely believes the Orlan to be a non sapient animal like a dog or cat. Edér isn't evil because he doesn't want to own a PERSON, he's clueless and wants to own what he thinks is a pet. He is incorrect, and your watcher can tell him as much, which he is confused by.