Hawaiian seems to put the verb first. If you want to use "akamai" as a verb ("to be smart") I think you have to put it first in the sentence. Following a noun like "kāne" it acts like an adjective modifying that noun instead. I might be mistaken, but I think your sentence, "This man is smart," would be, "Akamai kēia kāne."
I will try to put that in other words: To say "Akamai ke kāne" puts emphasis on a behavior, or better, a specific act like "The man is doing something clever" " ... is making a clever move" whereas "kāne akamai" would rather be used if you want to state that he "is a smart man" im generall (not only by a specific act). Did I get that right? Is that why we shall answer "This is a smart man" just as "He his generally a smart person" and not "This man IS smart" which rather states "This man acts smart (right now)"?