Anyone with a PhD Comp Sci from Harvard is automatically very smart in my mind, unless by "smart" you mean something else...
That is, people have clever _moments_ - some more than others perhaps - but can equally have stupid ones. We convenientally flatten the statistics into a boolean.
For example, recently someone considered to have made a lot of smart decisions in his life has been found to have payed others to rank his character up in a video game so he can brag about it. Everyone has stupid moments.