How many dudes you personally know
who are hetero and you know for a fact they have gotten HIV from vaginal sex. Your answer showed be zero. Are you with these dudes 24/7? No, I bet not. That is because a lot pf people lie about their sexual habits. It is estimated over 50% lie about sexual and drug use history to their doctor. Why should they tell you the truth? I can show you several studies that support this.
There are many, many, bi sexual, gay, ladyboys lovers, drug users who are in the closet. A lot who get it say they got it from hetero because they do not want the stigma or judgement of being labeled with another type of sexual orientation.
Many people I know are anti gay. If you got HIV it would be much more acceptable to tell them you dated several women and made a mistake not using a condom and caught it. They would feel sorry for your poor judgement. If you admit to gay they would judge with: Just another f-g pervert and probably avoid future contact.