Uhoh, button pushed!
"Smart" and "stupid" cover so many things, the words are almost useless now*. If anything goes wrong with your thinking process, it gets counted as stupid. It could be memory, ignorance, ignorance because you learned differently 50 years ago and have since forgotten, not taking the time to think through all the possibilities, not thinking of all the possibilities, not being able to keep all the factors in your head at the same time, and on and on.
Then we take it another step and pretend all of these factors are really one factor - being "smart" or "stupid." If you're good at one, you're good at all of them. If you're bad at one, you're bad at all of them. Hence, different people will be convinced that you're "smart" while others will be certain that you're "stupid" - all in the same day!
And then there's still another silly step - turning it around. Hey, I'm not stupid! I can remember the name of every kid in grade school still at age 50, can you? No?? Well then, I'm smarter than you so I'm right and you're wrong! <facepalm>
An IQ test measures a pretty small part of 'smartness.' It gives you every bit of information you need to solve the problem, so you don't have to figure out what is and isn't relevant. You also know that there IS a way to get to an answer, which you don't always get in the wild. The information is all delivered at once and placed in front of you, so if you forget any bits, it's right there to read again. They keep as far away as they can from anything controversial, so you don't have to worry about personal prejudices getting in the way. This is all stuff you have to deal with when thinking through issues outside of a test environment.
* except when you need to call a game stupid because it made you mad. That's TOTALY appropriate!