Black Ops Free For Xbox LIVE?

Uhmm I Dunno I Am Able To Play COD Black Ops On Xbox LIVE For Free, But The Thing Is I Haven't Purchased Any GOLD Membership And It's The Only Game I Can Play For Free Online, For Example If I Wanted To Play Guitar Hero Online It'd Say, I Would Need To Have An Active Membership, But When I Go To Multi-player Black Ops, I Go Straight Into A Pre-game Lobby No Problem, Is This Just Me Or Is Anyone Else Able To Do This? *Ps. It Isn't I Free Xbox LIVE Weekend As I Have Been Able To Do This For The Past Month Or So*