Should have read something like "... in the last boarding group you might have to check your carryon ..."
Example of boarding groups: On southwest they are A, B, and C with A boarding first.
Boarding groups vary with airline and sometimes model of airplane. Some frequent travelers go to great lengths to learn the boarding groups for each trip they take and select seats accordingly. When tied to seat locations, boarding groups are often called zones.
You do not have to go to the carousels to pick up gate checked and non-yellow-tagged bags before 10 PM but you do have to go to the Magical Express welcoming counter. ... If they are not experimenting with roving pre-welcoming CM's directing absolutely everyone to the bus queues.
Caution: Gobbledegook follows.
Sometimes zones look random such as
front 1 7 5 3 6 4 2 rear
which actually translates into rhyme and reason as first-class, back, middle, back, middle, back, middle, whose purpose is to get stowing going in the middle as well as in the back and speed up the boarding (like burning a candle at both ends for more light)