exactly as you say, Uwe. there is no need for worries, filenames are not being transferred. you can be spotted only in the case that a studio spy is actively connected to a swarm and you are actively leeching from him. ISPs don't inspect their customers traffic, they only receive studio appeals with your IP address and afterwards ISPs contact you to remove the content to comply with
rights.
ISP's in Canada have started to monitor torrent traffic in every way possible, look at Bell Canada / Sympatico, they track them, as well as throttle them.