LW2: You're WAY overthinking this.  It could easily mean that several of your ancestors from different family lines were Jewish a bazillion generations ago--it doesn't mean that one of your grandparents wasn't who you thought it was.  My family did the DNA test and was frankly astonished to discover that it completely reflected family lore: Everyone else we know has discovered either through the tests or through genealogical research that their families have either been fibbing or had no idea what they were talking about.  But it's really not a big deal (not that there would be anything you could do about it if it were).