Where I came from, I wasn’t particularly smart. This can be proven by many testimonies and reports of my former teachers. In other places it was different and so in the course of my life I collected very different assessments of my capability to think.
The reason is probably that there is not one intelligence, but instead many different kinds. Just as there are different kinds of skills. One person migt be good when it comes to juggling balls. Another one is skilled at combining words and yet another one is good at combining lines of computer code.
When I watch my nephews play computer games with others in a team spread all over the world. They are skilled at using a technique that was completely unimaginable just a few years ago. How would you want to evaluate these skills? In the grading system of my former teachers?