Why is my iPad causing WiFi interference?
I doubt highly that it is the iPad causing interference. What I could expect is that the base station at your friends place can't keep up with all the wireless devices at once. If the TV is using 802.11g as are the other devices that disappear and then your iPad using 802.11n then the base station might crap out. Have seen a few similar cases before.

Additionally some base stations have limitations, example older AirPort Expresses could manage 5 or 10 clients. Once an 11th device comes into the network then a device or two or more might be kicked out because of the DHCP TTL time out. Going static with your IP address won't fix this, only a better base station, eg. the newer Express or Extreme.