The point is quite simply the feature you see and mention is not the main point of the article.
Because that is not the part connected to the change, as related to these newer models...
The entirety of the article and the intent, is directed to the newer models that also use:
"When you use Find My Mac to lock your Mac, it also prevents your Mac from starting up by setting a
firmware-based password. As soon as it receives the lock instruction from iCloud, your Mac displays
a lock screen that has four to six blank fields.
To unlock your Mac, enter the code you created when you locked your Mac from the Find My Mac website.
If you forget or can't remember the password you set using the Firmware Password Utility or Find My Mac,
schedule a service appointment with an Apple Retail Store or Apple Authorized Service Provider. Bring your
proof of purchase (original receipt or invoice) with you. If you plan to visit an Apple Retail Store,
make a reservation (available only in some countries)."
The former means of defeating the firmware password that is stored in hardware is not feasible or practical
and authentic owners should have no trouble with getting help for the newer Macs at authorized AASP...
Also the tie-in with FindMyMac and other aspects of the firmware aren't the same in older hardware.
There may have been a firmware update to help certain older models accommodate this feature; however
if so the article does not imply anything for specific older models. So we can't take that as a blanket fact.
So to use a support article to form a hypothesis and then not choose to see how it applied to the new hardware
in the article, is a curious interpretation of the intent of providing those articles, of interest to newer product users.
Hopefully this concludes today's broadcast...
Good luck & happy computing! 🙂