AITAH for accidently exposing neighbour having a affair child?

I, 27F, take tutions for neighbourhood students in my free time. I was explaining the blood groups and how genes work to few of the students. These are generally smart kids and they like to challenge things when I teach them something new. Sometimes it turns in light hearted debates.

As I was telling them how blood group is codominant allels. Explained the table of inheritance and one guy went this is obviously not fully correct. When I argued back that its proven he told how both his parents are O blood group and he is A. I joked he must be adopted then, before telling him its probably a screwed up labs for one of them.

He obviously decided to share this knowledge of wrong blood type with his parents. Turns out he is a affair baby and father was hiding? a suspicion. She yelled at me and my parents and made a scene at our house because I ruined her and her son's life. I obviously didnt think cheating as a possible reason for this mismatch. My parents dont even understand how I exposed her cheating but they keep telling me I should not have meddled in their business.