Noob-ish question re: combat cards

Tonight my group sat down for our weekly game, and this was the first session that really included a significant amount of combat. (It should be noted that this is everyone's first time playing GURPS, and my first time GMing it.) At one point a certain player attempted to slam an enemy, but we quickly realized that the effects of Slam per the combat cards was ENTIRELY different from that given in the Basic book. Specifically the book says both people involved take damage, while the card says no damage is dealt unless the attacker crits his ST quick contest. So what gives? Are we missing something?

Noob-ish question re: combat cards