Gmane was not around first. Google Groups started almost a year before the gmane.org domain was even registered, and it was built upon the purchase of the DejaNews archives, which itself began in the mid-90s.
Deja News was a web interface for Usenet, not a newsgroup interface for mailing lists. I don't remember when google groups switched to a web/mailing list setup, but I think it was later than 2002 (when Gmane started).
