#inappropriatesongs

My 7yo daughter was singing an alarming song she may have learned from a school mate. How do I handle this?

This morning was kind of alarming. As both girls are getting ready for school, I hear my 7yo daughter singing in a calm voice but all of the sudden the song is saying "I hate myself therefore I want to kill myself". In a "la,la,la" sort of way...
I asked, “Did you make that song up or did you hear it somewhere?” She says that she heard two boys at school singing it and it stuck in her head. I asked if the teacher said anything and she said no, but I don't know if she even heard it.
Did I have the wrong approach to this?
Should I have said something different and if so should I bring this subject up again?
I don't know if I should mention this to the teacher, the parents of these boys or what. Help!