By 'stream US TV' I assume they just mean using popular streaming services like Netflix. If that's the case, than UDP multicast packets aren't involved at all, since it's all unicast.

Your advice would apply if they're using a local TV tuner or IPTV setup to share live TV on the local network or something, but that seems unlikely. But for content coming from mainstream Internet streaming services, it's good bet they're not using multicast.