Who the hell cares? Of course it's not "sex", that term is reserved for sexual intercourse. It is a sexual act though, and engaging in it means a loss of virginity. Losing your virginity doesn't mean vaginal penetration, it means breaking the "seal of purity" on your sexual history. Once you've engaged in any form of sexual act, you are no longer a virgin. That's all there is to it.

It's like opening a bottle of Snapple. You may not drink the whole damn thing, but the bottle has still been opened, and as such, it's purity has been compromised.