I don't understand how this can happen if we have not met

That would not be a problem. Twins are in contact through their higher selves, who don't need an appointment to meet. There reports of people who have met their twin in dreams or even have met a dead twin.

But there's not enough data here yet, what you describe may be twin flames' stuff or something else.

That person is a therapist, might be a healer, you are on semen retention, and also dwell on the Kundalini subreddit. Too much stuff that may account for what you describe here.

And there's no mention of spirit guides and the Universe telling that you are twins, those would be signs I would trust more.

And you were writing here at r/twinflames 5 months ago, which I'm guessing would be before knowing about this person: now I'm not saying it's your case but some people who are on the lookout for a twin may have the tendency to shoehorn a label to someone they meet.

If she is your twin things will develop in ways that will leave you with much less doubts.