It was already near lunchtime, so those cars were probably those that were planning to stay out of the south base for a while, as they didn't bother going out earlier so that they could also be back before nighttime.
And when they could finally see the south base, they also saw two cars ahead of them who were also going to the south base just like them.
The south base was in a flat area, so when they're still far, they could still see it after passing through the hill that was blocking their view.
Just like the north base, there's also a wide area around the south base that wasn't filled with any buildings yet, so they could still see a wide space before its walls.
The walls of the south were also obviously not complete yet, as they could still see some people working on them while they're still far away.
