They're in the Horizon, which means that none of this is actually real, but Steve does have to admit that it's a good shorthand for learning more about his fellow Summoned and where they come from. Garrus had told him before about his people and their interaction with humans in the future, when space travel allowed their paths to cross. Seeing it like this is certainly different than hearing about it, though.

He accepts the explanation without too much protest. "I've actually traveled into space once before, when..." He trails off. It came with a long, long story, and it hadn't been a happy trip. They'd tracked down Thanos only to find out that he'd already destroyed the Stones, and their chances of undoing his terrible decision with them.

Instead of dwelling on that, Steve turns back to the doors that presumably lead to other parts of the Normandy. "If we head through there, could we see it?"

There would still be something novel in seeing the stars from the perspective of a spaceship, even if Steve has experienced something like it once. He doesn't know how far Garrus' Horizon actually extends, though.