I would say that that's a redefinition/hijacking of a word that's been in use since long before 2008 to mean exactly "independent" in many different art forms.
EDIT: You may find it interesting to read Jordan Mechner's journals about the making of Prince of Persia as a solo dev (published by Broderbund, so not quite fitting the indie self distribution model today, but otherwise fairly similar). They used to be available online, which may not be true anymore, but it's certainly worth $8 or whatever they may be asking for.
Still, that's how the word is used today. Many, if not most, "indie" games are either made by those original TIGSource people, or were strongly influenced by contact with that community.
EDIT: You may find it interesting to read Jordan Mechner's journals about the making of Prince of Persia as a solo dev (published by Broderbund, so not quite fitting the indie self distribution model today, but otherwise fairly similar). They used to be available online, which may not be true anymore, but it's certainly worth $8 or whatever they may be asking for.