Need help explaining something

When I came out people said that some people already knew I was gay, and while they were trying to say that to comfort me, I didn't like it. I think it may have had to to do with internalized homophobia, or not wanting to be caught in a lie, but neither of those things really hit the nail on the head. Anyways, if you could shoot some ideas as to why I didn't like people guessing if I was gay or not, that'd be great.