Many flying objects go by that are unidentifiable, it would be foolish to assume that every single instance of any object that has ever flown has been 100% properly identified.
As for such objects with a non-terrestrial source, well it cannot be ruled out since the object is by definition never identified. I certainly do not take such matters on faith. Because if I did, I could just claim any far enough away speck as an angel or the tooth fairy or take any such nonsensical theory based completely on 'faith'.
Also, if I did identify such an object as clearly having an extra-terrestrial source, then it would no longer qualify as 'unidentified' now would it?