The first written mention is Kiev litopis that was way before the polish source, and it would be pretty pointless for Kievans to refer to themselves as borderland. I guess given the politicization of debate it's hard to find any objective info. From point of view of western neighbors it is possible that your interpretation makes sense but it does not explain why Kiev's litopys would use this name. On the translation some of words that have actual meaning are just transliterated which gave me the impression that it was google translation.