Is it normal people like me shy but not confident?

That is a fact. I am also very shy and I get so many friends because of it, it comes down to the point that since you don't talk a lot when you are acting shy, you listen, and that is what everyone in this world wants, to be listened about their life, problems, achievements, etc. I used to work in a restaurant where most employees would talk shit about other employees that also worked there, all I did was keep my mouth shut and work while others talked, this way I could easily figure out who had potential to become a true friend in my book and avoid problems with those that probably talked shit about me when I was off.

Maybe they find it easier to approach you when you're shy. Maybe they can talk about themselves more. Maybe they want someone to agree with everything they say.

Perhaps they are just not used to seeing you in that light.

If I may say, Fluck them. You need to get away from them and get to people who are happy for you for feeling good about yourself, because those people who hate your confidence are either jealous or plain douche-bags. Find people that will be happy for you and your accomplishments.

Maybe it is the content of what you are confidently saying that freaks people out.

It is difficult for people to accept changes. Talking with a confidence and giving your opinion is good and I suggest you to keep it up. Gradually people will start accepting it and they will respect you.
I wish you the best.