People who excel at mathematics use better strategies than the other; they don't necessarily have better brains. We teach simple strategies that can have you multiplying large numbers in your head, doing mental long division, even squaring and finding square roots of numbers off the top of your head.
And here is a secret. People equate intelligence with mathematical ability. In other words, if you are able to do lightning calculations in your head, people will think you are intelligent in other areas as well.
Here is one of my most important rules of mathematics. It is an unfair rule, but it is a rule just the same.
The easier the method you use to solve a problem, the faster you will solve it and there is less chance of making a mistake. The more complicated the method you use, the longer you take to solve it and greater the chance of making a mistake.
So, the people who use better methods are faster at getting the answer and make fewer mistakes. Those who use poor methods are slower getting the answer and make more mistakes. It doesn't have much to do with intelligence or having a "mathematical brain."
The methods are more than techniques for fast calculation. They develop strategies for general problem solving. If you don't know, or haven't been taught how to solve a problem, you will work out your own method.