They could also make agreements with ISP's where their TV's can be whitelisted for access to a public or potentially unlisted WiFi, enabling them to connect that way, without the vast majority of customers ever being aware.

Similarly, these TV's could connect to any open wifi hotspot it can find and phone home/download updates that way. Cox for example proudly boasts how more than 4M of it's residential customers modem+router+ap's can be used for "WiFi Hotspots" by anyone - not just the customer/resident - if they have a cox account. I don't see why Samsung or any other manufacturer may approach said ISP's to use this network to update devices under some guise of "convenience" or "seamless updates" ostensibly for their less tech savvy users.

I don't know if these business deals exists, but "smart devices" will often try to phone home/update anyway they can, even if you don't manually configure it on a private network.

EDIT: Forgot the source on the cox hotspots claim: https://www.cox.com/residential/internet/learn/cox-hotspots....