Himyar didn't exist in 272 BC either, it wasn't until about 100 BC that it became a player in South Arabian politics and wasn't the dominant kingdom until it conquer/merged with Saba between about 25BC and 50AD (it was a rather complex, erratic process it seems). Also, at the start of EB the civilization in Ethiopia wasn’t particularly advanced or unified. Culturally the coastal region was under the domination of Saba (on and off politically too) and it wasn’t until the late 1st century BC that we start to see any sort of advanced, unified state (this is the Aksumite Kingdom). Even then true height of Ethiopian power doesn’t really happen until the victory in the war with Himyar in 525AD. To be far this was an advanced Ethiopian state before EB time’s frame too, but that collapses in the 5th century BC.