"그는 가운데에 앉아요."
Translation:He sits in the center.
It's not middle (중), it's the center of something. Center implies 3 dimensional space. Middle implies 2D space. You can be in the middle of a crowd but not in the center.
Yes, there are overlapping idioms. But, middle and center should have different usages.
Isn't 그는 gender neutral? Tried "She sits in the center" and it wasn't accepted...
It’s supposed to be gender-neutral, but this course is teaching English speakers, who are accustomed to gendered language. And so the Korean neologism, 그녀, for female is used.
No, in this sentence, 그 means "he" and 그녀 means "she." 는/은 is a topic marking particle, which gets attached to the subject of the sentence if the subject is a new conversation point or your are drawing emphasis to that subject.