I think you're talking from a human point of view, but you know nothing of the similarity of Antarctica compared to the other continents for this hypothetical s

I think you're talking from a human point of view, but you know nothing of the similarity of Antarctica compared to the other continents for this hypothetical sentient species we're talking about. If they can't bear positive temperatures then all other continents are totally out of bounds for them, while Mars isn't. That's different from the reverse, in that even if we can't naturally live in negative temperatures we can easily enough wear warm clothes and heat up the spaces we live in. Same reason we find nearby Venus uninhabitable but faraway Europa seems almost colonisable. Of course there wasn't actually an Antarctic industrial civilisation, but that's not really the point. Also, any evidence would be found either under 2000 meters of ice or at the bottom of the Antarctic ocean, so we wouldn't know about it yet.