Antibodies to other (unknown) viruses are one potential explanation of some false positive HIV test results. There can also be observer error and testing error.
okay. That makes more sense. Well, the rapid test is more prone to a false positive than other tests. They never assume positive from that and you will do a lab test next. Is that not what the nurse said your next step was? I would go to either a doctor or a reliable lab that does this. Really, you had at best a low risk and I'd be surprised if you were HIV positive from that. HIV is much harder to contract than people think. But there is nothing anyone here can tell you until you take a new test.
Take a deep, calming breath. Your anxiety is amped up super high and needlessly. Have you actually tested and gotten this positive you are asking about? Or are you in hypothetical territory here? If this is all just anxiety about going to take a test then it is needless and undue worry. You barely had a risk if you did at all. And a one time sexual encounter is low risk if you did actually have a risk (which is questionable). So, relax.
Yes she was right. Nobody is declared HIV+ on the basis of a single test, it has to be confirmed through other tests. However result of the test depends on the risk. If risk did not exist, results will always be Negative