He more likely could have contacted HIV virus infection with unprotected sex. The HIV virus is detected by special blood tests. Yes, the AIDS virus is HIV, but HIV patients can avoid AIDS by taking the HIV medications, or by not developing any illness (AIDS) for a long time.
Again AIDS is diagnosed as illness (caused by HIV virus) only if patient shows at least 2 opportunistic disease entities. After patient gets sick with these certain disease, then if needed AIDS would be confirmed by positive HIV test.
The HIV virus destroys immunity cells; thus opportunistic disease occurs at some point. This is AIDS, diagnosed not by blood tests but by the presence of certain diseases we would not get if immunity system is functioning.
see-
http://www.cdc.gov/hiv/resources/factsheets/