I experienced that when I search users I also get listed some that are not at all similar to what I search. Due to presence of some other utf-8 characters I Guess that clue could be relate dto that. Please check attach when I searched users with name Nikola.
I think it searches users first names, last names, email addresses, and eventually other user settings/fields as well, if they contain the given string in lower cases i.e. “nikola” in your example. So all users from your result list I understand, except “Srdan”, but maybe that users has somewhere in his metadata this string as well?