Title explains it mostly. When I run dmg2img -l BaseSystem.dmg, this is the output:
dmg2img v1.6.7 (c) vu1tur (to@vu1tur.eu.org)
BaseSystem.dmg --> (partition list)
partition 0: MBR
partition 1: Primary GPT Header
partition 2: Primary GPT Table
partition 3: Apple_HFS
partition 4: Apple_Free
partition 5: Backup GPT Table
partition 6: Backup GPT Header
This is the expected output (from the guide): https://dortania.github.io/OpenCore-Install-Guide/assets/img/unknown-20.7e0e5028.png
It is probably due to update to dmg2img, not because of Apple. These are actually present in the expected output (inside the parenthesis), with more information that causes confusion to beginners. It should be updated to avoid confusion.