Some instead assert TVs might connect to the first open network available, like if a neighbor briefly opened a hotspot, which sounds more believable.

I haven't seen an open network around me or anywhere I go in years. Even places like gyms, coffee shops, and restaurants require passwords typically.

I think it's much more likely TVs make deals with cell phone companies and offer hardware that only works with their cellular service. Many pay more than $100 a month on their phone bill to pay off a phone. People might accept another $20 or so for a large screen TV with bundled apps-costs can be kept down for the carrier with ads and tracking that can't be bypasssed as it will use the carrier's network connection.

Both theories would be easily testable. The danger is also much smaller if it's not on your Wi-Fi regardless.