Read slower. He was claimed off waivers before becoming a free agent. The Spurs didn't have room to claim him so Hickson was technically never available for the Spurs to sign.
That said, I was DEAD WRONG about Hickson. I thought he was a scrub after the way he flatlined in Cleveland and then sucked horribly in Sacramento. It turns out that he was stuck in toxic situations and was able to rebound almost instantly once he landed in a halfway competent organization. I don't think he's as good as his numbers say (his defensive rotations are still slow and he doesn't really protect the paint like you want from a center) but he's definitely not a scrub and probably has a value of $6-8M per year.