HIV Seropositivity?

Question

Does this mean that a person has a certain antibody in their blood that causes them to be immune from HIV?

Answer 1

No. It means that HIV antibodies are present (which would happen, for any disease, after infection or immunization). In particular, blood tests serpositive after seroconversion, which is "the development of detectable specific antibodies to microorganisms in the serum as a result of infection or immunization" (according to Wikipedia's article on seroconversion).