Look deeper into the meaning of 생기다: to be formed, to appear, to happen.
The ugliness is a trait that emerged/happened in the past. Consider the expression: her face is disfigured. Disfigured is in the past tense. Although the trait of the disfigurement is ongoing, the statement is about a past event that caused it.
The Anglophone mentality is that the person is “uglying” (present continuous). The Korean mentality is that the person became ugly at a past point in time and that ugliness carries into the present where a person making an observation will simply say “hey that person became ugly at some point in the past!”
I wrote more here: https://www.duolingo.com/comment/24492618
It's in past tense. The sentence is asking who is ugly, but ugly is in past tense. When you are describing someone, you state their appearance in past tense because they are already handsome or ugly. I hope that makes sense. It's a little confusing.
Oh yeah is quite alike to say who is scared, ugly in the past tense it is the same ugly, so when we say who is ugly we are alredy making a past tense sentence, right?