False positive/Indeterminate HIV status?

Today I went in for HIV and took an oral swab/Rapid test which gave me my results back in 20 minutes. The results came back preliminary positive. At which point they took two blood samples and ran two more test. Both of these tests came back negative. However they sent the second blood sample, along with another oral swab to the lab for testing to give me a definitive answer. I'm just wondering, how likely is it that my first result was just a false positive if two of my other tests (which were done on site) came back negative? Naturally, none of the volunteers at the clinic would say other than that my status was Indeterminate.