A solitary request by a standard users IP would NOT be a valid request.
Depends whether "standard user" means someone who has already set foot on the site and established themselves as human. Heck, I once got a request for "humans.txt" ;)
Yesterday got one from 18.104.22.168 for BingSiteAuth.xml
That's the standard Bing wmt file, like the google or yandex versions with all the numbers, from the now-standard IP for this request. I don't know when exactly they transferred this task to the 131.253 range. Somewhere between early June and early November, based on before-and-after around a big hole in my logs.
Much of the worry goes away when you add to htaccess something like
Header set X-Robots-Tag "noindex"
(adjusted for any non-page extensions you may happen to use) because really I'm more worried about google indexing my robots.txt than about malign robots reading it :)