they sold it, as most people would to erase their streaming service credentials.
Your appraisal of consumer security awareness is way too optimistic.
Most people would just sell the TV. It's uncommon to seem them also reset to default aside from tested units sold by some secondhand stores that clean up used gear before selling.
Streaming services; assuming an old TV was even used for those; normally detect if a device has gone unused or moves to a different ISP or geolocation and cancel the device token requiring a revalidation. The old TV's reason for being for sale might even be that Netflix, etc, revoked their compatibility with it due to its age or outdatedness.
Anyway. There is never any presumption the seller factory defaulted their TV before selling it.
The manufacturer can log the EULA acceptance, and they will most likely be able to report on exactly the date, time, and IP address when someone clicked Okay. In the case of a dispute; the onus would be on the manufacturer to show evidence that the customer agreed. That is if the customer disputes the alleged fact that a EULA was accepted by them.