Statistically, they likely had a false positive the first test. Columbia University commissioned a study on 50k people in Qatar (covid spread was rampant there) who were confirmed positive, and after 7 months, catching and recovering from it provided immunity at a threshold exceeding the Pfizer vaccine.

Yes, there are people who have caught it twice. They are rare, and the paper highlighted that a likely explanation was false positives in the original testing.

I'll take the vaccine, but shouldn't be required to.