I'll add to this... I've now done some digging.
This wasn't even really a hack. Well, I wouldn't call it one. It was "someone left the keys in the door and someone else turned them".
Apparently from what I can gather, the issue was that the controllers in the refrigerators have a web interface. They don't connect to a cloud, you connect to them directly... and this is where we find the keys in the front door.
The installers don't know how to ask for IT support and don't know how to get internet connectivity sorted out. They had a much better idea... install a 4G router and open the port for the controller on a public IP address. And this is important too, because more or less every LTE/5G provider on earth uses CG-NAT and IPv6. You'd have to pay extra to get a public IPv4 address but compared to the cost of a managed refrigerator, this was a trivial cost. The installers did this specifically because to give the customer access to the web interface, they would need a public IP or an open port.
So, you have a basic controller running a computer approximately in the same category of an Arduino.. maybe a Raspberry Pi Pico... running software written by people who were focused on the operation of the refrigerator rather than IT security. And there are no software updates... if the fridge works... it works.
Next issue, these ARE NOT IT PEOPLE and the people making the controllers ARE NOT IT SEC PEOPLE. There were default passwords. Things like admin/admin.
There were no firewalls. And Samsung is much more secure because it connects out to cloud which is centrally secured (or compromised).