The thing that would bother me about this is that you only know what's being blocked; you have no idea if other spyware is getting through because your pihole just doesn't happen to know about another domain in use.

The only surefire way to block it would be to put some metal or foil around the wifi antenna (or disconnect it entirely, if possible). Otherwise the TV could connect to any random open wifi network it might find (assuming there is one in range). Even if you connect it to your own network and block all its traffic, it might just decide your network is broken and find another one.