This happened to me. After they left, I tried a factory reset, but I don't have confidence there's not some code to remember previously saved wifi connections because my tinfoil hat is firmly in place. However, as you've said I only use the TV as an HDMI receiver. None of the TV's apps are used again. So I'm not sure how much they can detect from just the use of the HDMI port as the only thing being used. The games we play to get the subsidized pricing.