This common argument for atheism commits what is known as the "genetic fallacy", i.e. attacking a belief based on its origins (or the perception thereof). We'll ignore the fact that one's birth country does not automatically determine their faith (there are Catholics in Pakistan, there are Muslims in Poland, and Dawkins himself is an Evolutionist living in a country that was once mostly Christian). Let's use the map I placed below Dawkins' tweet as a demonstration. Throughout history, there have been many ideas about the Earth's shape. The map isn't real, it's just there for purpose of illustration.
You will notice I've labelled each continent with a randomly assigned belief about the shape of the Earth. America believes the Earth is round. Africa believes the Earth is flat. Europe and Russia believe that the Earth is sat on a turtle. Antarctica doesn't even believe Earth exists, and Australia doesn't care. So, let's imagine Dawkins is a cube-Earther, and he uses the exact same argument:
"Round-Earthers, if you'd been born in Europe, you'd be a turtle-Earther. Turtle-Earthers, if born in Africa, you'd be flat-Earth. So why so confident in your faith?"
Doesn't work, does it? It doesn't work for multiple reasons. First, even if my map accurately portrayed the distribution of beliefs about the shape of the earth, there would still be some dissent within these countries. Second, who cares? Truth isn't determined by belief or lack thereof. The Earth is round, so even if this was a mostly American belief, even if every other country in the world had a unique view, even if not a single human being on the Earth believed the Earth was round, the Earth would continue to be round. In much the same way, Christianity is true. It doesn't matter which countries traditionally associate themselves with other religions. It doesn't matter how many religions exist. It doesn't matter that Christianity is becoming a minority faith (which the Bible says it will towards the end anyway). The truth cannot be changed by belief or lack thereof.
Now for the final nail in the argument's coffin. It backfires. See, while atheists tend to believe atheism is unique, it isn't. It's just as much of a religious orientation as theism. It takes just as much faith (arguably more), and it is subject to the exact same intellectual standards as every other belief. No free passes, no loopholes, no special status. So, Richard Dawkins: If you'd been born in Pakistan, you'd likely be pressured to be a Muslim. If you'd been born in Poland, you'd have a statistically high chance of being Catholic. Why so confident in your atheism?
To answer Dawkins' original question, I'm so confident in my faith because it is strongly backed by observable reality. It is historically sound. It's scientifically sound. It accounts for logic. It accounts for our existence. It accounts for the inherent sense of justice we all instinctively feel (even atheists). I could write whole books about why I am so confident in my faith. Here is a brief case I wrote a while back. Suffice to say, I would rather believe a religion with so many reasons to believe it than reject it because some dude in India prays to Vishnu...