You are not an end node, so nothing but encrypted data is passed between a Tor user and another Tor node. These bridges help people in countries who block acces

You are not an end node, so nothing but encrypted data is passed between a Tor user and another Tor node. These bridges help people in countries who block access to the tor network enter the Tor network. They don't use you to access any actual content. That said. Don't go to websites that put the iframe in if you don't want to be one. It's not like it's going to be a common practice to throw that on your webpage.