German Urheberrecht explicitly states, that downloading something is legal, if not downloaded from an obviously illegal source ("offensichtlich illegale quelle"). Thats why it is perfectly legal to download copyrighted music from youtube (because Youtube is obviously NOT illegal). Youtube ToS are irrelevant in that case. You are however still not allowed to copy the data (music) to a third party (that is when copyright starts).

Whether or not the file you downloaded was even allowed to be uploaded to that website, is irrelevant in that case. Then the uploader and provider are liable, not you the downloader.