One thing that doesn't seem to be discussed a lot in this thread is that the keystrokes alone don't tell you what Safari will do. The second and third cases of the original video show Safari adding extra characters (the second and third phone added "m" as in "realty.com[m]", and in my testing, "sketch" added "rs" as in "sketch[rs]". When I tried (iPad Safari) "realty.com", the "Top Hit" was "realty.com" and it did not autofill anything, and I got to realty.com (no problem there). However, The first phone in the video did not show any extra characters. Is Safari considering it a "search autocompletion" but not showing any extra characters, perhaps because they are suppressed?
Also, many commentors here report this not happening for them, but they do not specify the state of Search Engine Suggestions and Safari Suggestions options on their devices. My testing was done with all the default options (which is both Search Engine and Safari Suggestions are turned on)
EDIT: Could it be that the Suggestions system is taking the autocomplete candidate ("sketchrs" and "realty.comm") as its input (instead of what the user actually typed)? That would explain what I've read here except for the very first iPhone in the video...