The link does not take you to the story, so I have not read it. They probably mean that it is an old geomorphic surface: the land surface is old; the rocks need not be especially old. There are some ancient surfaces in the dry valleys of Antarctica...west of McMurdo basin int he Transantarctic mountains. The climate there has not changed too much in 15 million years, and I forget whether there are surfaces there about that old or if ice sheets occassionally have made a fresh surface.

Chris