As written, it applies to the "music, sounds, text or information that you make available or create whilst using the Service" and gives Flat a "worldwide, nonexclusive,
royalty-free and perpetual licence to use, copy, reproduce, distribute, adapt, reformat, modify, publish, translate, licence, sub-licence, and exploit the User Content
anywhere and in any form." [1]
I can see why artists might be a little concerned about this.