Personally, I find intelligence as the ability to survive in a habitat given. Humans are very intelligent in this aspect. Although we kill eachother all the time, there is still an ever-growing rate of people flowing into the planet. By working together, we're making the population grow.
As others have said, there are a lot of "stupid" people because they don't use their potential. Take the poor. They could make surviving much easier, but they didn't use their intelligence to help them get far. So they lead their life struggling to get by and have a family to carry on their name. But wealthier people (middle class and upper class) used what they could, to do what they could and they lead a typically more suitable life to raise a family for.
This doesn't mean some are and some aren't intelligent. It's just whether or not we want to survive or not.
I don't see why people are saying we're smart because other species are below us. That's not what was asked. He was just asking if humans were smart. We are.
But most animals are as well. They've adapted and evolved. Some better than us to survive. Just because we can recollect memories and develop tools to help suit us for survival, doesn't mean we're superior.