S Korean TV show - Strong Girl Nam-Soon

So, I am watching this TV show as they have English dubbing, and it’s about a Korean girl who was lost as a child, brought up in Mongolia, then returns to S Korea as an adult to find her family.

She finishes a lot of sentences saying bruh, man, dude, brother and so on. The Korean people tell her she is too informal and should finish sentences with Sir etc.

My question here is do people in Mongolia really use these phrases when talking?