"Can't judge a book by its cover" is not an aphorism, it's an idiom.
What you said was "To use the word "book" when what you mean is "person"". This is incorrect. I meant no such thing. I was referring to the slackware.com web pages (which can be considered a type of book, if you squint). True, I extrapolated the "man" part from yours. My bad.
If the idiom is wrong, clearly your would have no problem purchasing a book based on the cover alone. Can I interest you in a near perfect, signed by the author in 1926, first edition, first printing Winnie The Pooh? I'll mail you pictures of the front & back cover, and the spine. That'll be all you need to verify my US$5,000 asking price is a good value, right?
Clothes do NOT make the man. Shakespeare was a bawdy Elizabethan playwright, not a great sage or oracle. Clothes are just a tool, no more or less than a screwdriver or a typewriter. For more on my view on the subject, see this post.
But whatever. Clearly you have a pet peeve that isn't shared by the vast majority of the English speaking world. Hopefully you'll understand that I choose to bow out of helping to enable your quest. Enjoy the private crusade.