They say “always read the fine print”, well, here’s the fine print:
– Book in qualifying fare classes so that members can use their companion benefit. These include all Business Class fare categories and Y, B, M, K and H economy class fare categories. The first four economy class fare categories are generally higher in price descending from Y to K. The category ‘H’ was added to make it easier for card holders to qualify for a Companion Ticket. The reason why only certain classes have been chosen to qualify for this benefit is because the fare classes Y, B, M, K and H are more flexible and some have no penalties.
The rest of the jargon, you can read here: