Restoring custom packages after upgrade


I'm doing my first firmware upgrade and followed

I installed Opkg extras and Hotplug extras. I did 'opkg save', then downloaded the complete configuration tarball via LuCI, then flashed the file

After rebooting the new firmware, all settings are still there, everything is working. But afaik I would need to restore all my custom packages via 'opkg restore' now? But all packages like travelmate, vpnc, etc. are still there, eventhough I confirmed the new firmware version is up and running. Why? So restoring custom packages as described in the documentation is not required anymore?

The upgrade was 19.07.3 to 21.02.2. On #openwrt@OFTC I was told that such big upgrades always need a wipe and new configuration. So I wonder that everything is working fine, all devices, wifis, even additional packages like Travelmate and vpnc. Some LuCI tabs have said they run a migration at first call. I did not even import the configuration backup.
How can that be?

In the past I always did opkg list-upgradable | cut -f 1 -d ' ' | xargs opkg upgrade which I now learned is absolutely discouraged to do, and I won't do it in the future anymore, only for special additional packages.