Experienced a new boarding scheme on a SEA-ANC flight today. Have any of you seen this yet?

1. First Class/MVP Gold/Delta Top Tier
2. MVP/Other Delta Elite/Row 6
3. Passengers not using overhead bin, meaning all carry-ons can be stored under seat.
4. Rows 20-35
5. All Rows

On second thought, #4 may have thrown me off due to a longer than normal (for me) 737 being used. But, it was the first time I heard #3. Anyone else hear #3?