It was too good to be true (so David was right)!
I called the "library" in question and had a chat with a senior person. He told me that they had hired 5 students to go and "hunt" for new talents on sites like Metapop, SoundClick, SoundCloud, etc.
Unfortunately the guy who contacted me got a bit creative with the terms and offerings. What he should have written to me was that they would like to offer me a spot in the library and IF they manage to licence my song to somebody they would pay UP TO 200 euro. In other words that could also be 1 euro.

Still they want me to give them exclusive publishers rights for 5 years - this would mean that I cannot use (or sell) the song in other places for the next 5 years - even if they don't manage to licence it to somebody.
I politely said "No, but thank you".
Thank you to all of you for giving me good advice and turning on the "red alert" buttons inside me.
I got a lot to learn about this business!
Will
NB: Before somebody is asking about the company's name: I don't think the Library (which is German) did anything wrong on purpose, so I don't see any reason for publishing the name here.