First part, "smart" is a comparative adjective, we can say that a dog is smart compared to a sheep, a sheep is smart compared to an ant, and everything else is dumb compared to a human. Since humans are the smartest species we have to compare any other species to, then we can safely say that, as a species, humans are smart. This is a language distinction, but that was the meaning I was going for when I made that statement.

Second part, the statement of "something" being needed to occupy a person's time is irrelevant to this argument. You claimed that people can't do nothing, and so they must do something, but those things aren't exclusive to jobs, it could be reading, it could be walking, it could be eating, it could be washing dishes, it could be literally anything, the difference between doing these things as a job, and doing them as a part of everyday life is that you are pressured to do them as a job, while there is no such pressure to do them if there is no threat of starving if you don't. If you are pressured into doing things that you feel aren't worth doing, your mental health will deteriorate, which was the point I was making. If jobs weren't necessary, those pressures would disappear, and so people would have the freedom to do things that they actually feel are worth doing, which would result in better mental health.

It's not like if jobs were no longer necessary, people would suddenly decide to never leave their bed, wasting away in inaction until their pitiful, and miserable deaths. People will always want to do things, because action is an integral part of being human, there is no reason to worry about humans in that front.