There's gotta be a bit more subtlety going on here. DHCP leases include a lifetime:

    $ ip address show dev br0 | grep -m 1 valid_lft
           valid_lft 69133sec preferred_lft 69133sec

It's possible that older versions of macOS persisted the lease details across reboots and reused unexpired leases on subsequent network reconnections.

I am also fairly sure that I have never personally seen any evidence of any OS doing this, including macOS, including when it was still called Mac OS X. I suspect macOS simply brings up its networking stack earlier in the boot process, so the network connection is more likely to be ready and waiting by the time the desktop loads.