If Page Views = 0, then it is from s.tl() call i.e. Download link, external link, custom link etc.
thanks for your answer, but I'm still wondering what's the true meaning for my question.
Arun is spot on here. You can validate this by adding another metric besides page views, such as visits. Custom link calls do not collect pagename, nor do they count towards page views. The data still technically exists though, and it needs a row to display that data.