The built-in support for KML only loads points and polygons.
But you can load it as xml, rename file and then add some brackets to make it a proper Sense geometry like this:
'[[' & replace("LineString/coordinates", ' ' , '],[') & ']]' as line_geom,
(XmlSimple, table is [kml/Document/Folder/Placemark]);
The railway kml file is borrowed from the City of Vancouver