This just denotes the 'new' expanded cardridges with a game using a 4 KiB ROM. They are also known as 'Challenger Series', include titles like UFO (Astroids) or Freedom Fighters (Defender).
While the external address space was limited to 2 KiB, the cartridge port did feature two select/address lines, so up to 4 ROMs with a total of 8 KiB could be added without further tricks. Still, early games did fit well in just one ROM. It wasn't until 1981 when UFO/Satellite Attack (#34) showed up as the first game requireing two ROMs (4KiB).These games where marketed as 'Challenger Series' and often hyped with the 'Expanded Memory' claim you noticed.
(BTW, your G7000 got 192 bytes of RAM - there are additional 128 bytes for the screen data :))
Addendum: William Cassidy great Odyssey² Homepage! has it covered with a seperate FAQ entry: What is the Challenger Series?. Prime source for information about Odyssey2/G7000 anyway.