Grammatically, both can be used in the sentence, however the context seems to indicate the question was looking for the word wise.
Actual means literal or existing in fact. While words and ideas can be literal or existing in fact, the word actual usually appears to emphasize the literal nature of the concept being described. For example, actual income would emphasize that the income is existing in fact, compared with, say expected income. This type of emphasis is not indicated by the sentence, and thus the word doesn't really fit.
Native speakers, in my opinion, would not use actual in this context if they were trying to say Justin was a very literal fellow, but something like realistic, concrete, or constructive.
The word wise means informed, educated, or showing good judgement. Words and ideas can be wise and this works well.