I find it tiresome that we must have representation for the "good" exceptions of all the evil races. It's okay for the illithids to be mysterious evil shady bastards, that's their whole appeal. By humanizing them you basically dispel their mystique, and yes, by turning him into this helpful creature you did just that even if he had an interest in observing you.
Good specimens of an evil species are so rare that you are supposed to be able to rest easy about killing them without a second thought.
This is not a species issue - it's an example of a balance in characterization generic to much of what we call drama, and a long used technique in story-telling. In a romance, you will have the suitor with good intentions v one with bad intentions. In an action movie., it may be good spy v. bad spy, or good cop v. bad guy. Lord of the Rings have Good Wizard v Bad Wizard. Here we get Bad Illithids, and the "badness" is reflected by an example of a "rare" Good (or at least less bad) Illithid.
